you may save a few watts by 2x drivetrain efficiency but look at the wasted aero potential with your legs 
However, I’m in the 2x camp as well. One of the reasons why I don’t like riding my MTB is this 1x thing. How I miss the 3x 1990s. All an evil industry plot to sell us more bikes.
And of course, my gravel is 2x. Di2 is simply too nice.
Hot take. If you prefer 2x (or 3x) you’re not really mountain biking 
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Of course everyone is mountain biking, and they’re all awesome, but I don’t see 2x on any technical terrain these days.
Met my wife when I already was a “cyclist”. Actually met her while cycling. She’d probably be highly irritated if I suddenly showed up with hair.
I live in the Alps. I don’t see an bikes at all anymore. Only E-Bikes. They’re everywhere. Everywhere.
Or 1x allowed engineers to make better full suspension designs, and as a result, 1x became the industry standard.
You can’t pick chainring sizes on 2x and 3x? 
Fewer people change them because they are more expensive. Seriously, I paid way more when I had to replace chainrings on my 3x10 than on 1x. And they didn’t last 3x longer. Definitely don’t miss my FD on my mountain bike.
PS I think the ability to choose a suitable chainring to adjust your gearing is a godsend. Yes, this is possible on the road — to some degree, but IMHO the gearing of most road bikes is still too hard for people who are not at 4+ W/kg. Shimano only offers two chainring sizes on GRX 2x — not enough in my opinion, and certainly not easy enough.
I was a bit of a 1x hater on gravel for a while because I was a diva about the bigger jumps between gears, but I don’t even notice the gaps anymore. I’ve done quite a bit of gravel racing on 2x (sram axs road 12 speed) and 1x (both explr axs and mullet eagle axs) and I’m pretty much only on 1x these days. I’ll run Eagle if I need huge range (borrow the RD from my MTB) and explr if I don’t need quite as much range. I agree with prior comments on the efficiency, you are seldom in the 10 and you are not typically pushing hard when you are. Assuming you ride in the middle of the cassette most often, you might even make the case that a 1x (a centered front chainring) is more efficient than 2x (staggered chainrings). Or at least close enough that it’s a pointless debate. There could be some courses where 1x hits a limitation on top end gearing, but my experience is that I’m never gonna get dropped by spinning out. I run my 1x (42 w eagle 10/50 currently) on our weekly team road ride and I’ve never been dropped due to gearing. It’s no problem into the low 30mph’s and there just aren’t that many places where you are going 35+ for extended periods (where you can’t tuck and draft/coast). You do need to paying a little more attention not to get gapped on downhills, but not a big deal. Dropped chains aren’t an issue for either as far as I’m concerned. I might give a slight nod to 1x with narrow/wide chainring, but you’ve got the FD cage on 2X that should prevent any serious drops there. Bottom line - both are totally fine for gravel racing. The tire clearance issue with 2x is the biggest “real” factor in my opinion (on courses where you want to run bigger tires). The rest of it is just noise and basically a religion discussion. Oh yeah, and Keagan is typically running 1x (mullet eagle for unbound last year) and he seems to be doing OK and we should all copy what the pros do.
Sweet ride ever hit any sick jumps?
GRX Di2. I do not have to think about shifting between rings. One button gives me more gear, the other button gives me less gear. I think I’ve dropped my chain two or three times with two of those being caused by my own error that caused the chain line to move inboard too much. (missing thru axle end cap)
That’s the same top gear I have on my aero road bike (42-tooth chainring and 10–36 cassette). I spin out at 63–65 km/h. I only use the 10-tooth gear outdoors when I go downhill, and then I’d almost always restrict myself to <= 70 km/h for safety reasons (I’m no SAFA Brian). On flat bits, it doesn’t matter one iota. I might get a slightly larger chainring if I were living somewhere flat.
I remember an interview of someone who was consistently at the front of Unbound, and he raced on 1x and 2x depending on sponsorships and preferences.
IMHO it is almost entirely personal preference, only in some edge cases is one setup clearly the better choice. In the long run, though, I think we should expect to see fewer and fewer front chainrings. The compromise with 1x13 is quite minimal even on a road bike. With 1x14 I reckon a FD is no longer needed. After all, there is a reason why we went from 3x to 2x …
Not in terms of shift logic, but you do have to ease off power when you are shifting in the front. Front shifts are never as seamless as shifts in the rear. Knowing when to (not!) shift in the front is a skill if you live somewhere hilly or mountainous.
When I’m going small to big, it’s almost always because I’m picking up speed, so in those rare cases where it just doesn’t catch right away, backing off doesn’t cost me anything. I also have my Di2 linked to my Garmin so I get a beep & on screen pop up when I click into that last gear out back before the front is going to shift, so front derailleur moves are never a surprise.
My justification:
I spent so much money on my 1x setup. Do I regret it? yes, wish I had 2x, but not prepared to take a huge loss for the change
Backing off needs to be timed e. g. in races when you crest a short hill and need to stay on the power to not get dropped. I’m not saying it isn’t possible, I have been riding with front derailleurs most of my life, but it needs to be timed correctly. On casual rides, this is less of an issue, though, apart from feel.
To me the biggest advantage of electronic shifting is that electronic front shifting is much better. If you do this mechanically, it is really a bit of a skill to shift up in high load situations. Still, it isn’t seamless, you gotta pay attention to your gears.
I’ve had two gravel bikes, one with 2x GRX 46/30 & 11-40t cassette and my current bike’s setup is SRAM Force / Eagle mullet 1x with 40t and 9-50 cassette. I’ll admit that the GRX setup I ran had more low end range, but I absolutely love the simplicity of the 1x system and when I’m on my limit feel that 1x gear selection on steep or technical terrain easier to think about and execute. I like the 1x setup so much that I have thought about switching my road bike that currently is 2x Dura Ace Di2 to Sram 1x.
This is the most important comment yet! All these data points are done with a perfectly clean drivetrain in ideal conditions…conditions you see at the starting line and never again for another 100 miles. 2w savings but carrying a hydration pack with bars that flair to 46+cm. Seems odd to me that people lose sleep over a watt here and there on drivetrain efficiency but completely ignore aero loss, which is orders of magnitude greater over gravel race distances.
My answer is have a justification for what you run and run it. I use a 1x simply bc my “gravel bike” is really just my cross bike in the off season…I run that 1x and i dont feel like the added effort/cost of having to run a new derailleur and a 2nd crankset. I use a 42T paired to a 11-42 out back. I casually ride gravel with friends and did 1 event last year, maybe will do 1 or 2 this year. Not interested in dropping a few grand on another bike to get used a few times a year
I have had 1X and 2x grx.
I like the 1X for how simple it is. 2x is great but it makes me think, so I need to shift down in the rear. How close am I to the top of the cassette, what if I try to big ring and then need to shift. It’s ok to mess up on a training ride but in a pack at a gravel race it’s nice to just choose a bigger or smaller gear
This is a terrible plague
Same can happen on a 1x drivetrain.
Fun to watch in VC‘s last video (min 14:30).
I’m racing since the 1990s. 3x, 2x, 1x. While clutch mechs and narrow/wide have improved drivetrain reliability a lot, in very muddy conditions you’re simply lost. I ride 1x ever since Eagle came out, dropped my chain so often when it got really muddy in races.
However, what is a little bit odd in the video, the drivetrain does not look so bad. And that he drops the chain so often. Of course, it’s hard to judge from a distance but based on my experience things usually look worse.
I wonder if he was just unlucky enough to manage to put the narrow chainlink on the wide sprocket tooth every time…?