Might have already been mentioned but Josh Poertner covers the 1x vs 2x debate on most recent Marginal Gains pod. TLDR: 2x for all but the flattest courses. RIP my 1x Aspero.
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I went with a 46t chainring. Got 11-40 in back. Works well enough for me, keeps me pretty much mid cassette. I don’t have a lot in the way of hills though.
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40:11 = 3.64 is a very different gear than 40:10 = 4.00 > 50:13 = 3.85 or 42:10 = 4.20 ≈ 50:12. Sounds like you were undergeared to me and you should have opted for a larger chainring and different cassette 
Oh for sure - not ideal gearing at all. I still don’t think it’s wise from an efficiency standpoint to be spending a significant amount of time in your 3 smallest cogs which could still be the for a lot of folks using 40 or 42t rings even with 10t cogs. You’ll be using that 11 and 12 way too much.
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Not in my experience, although it depends somewhat on your self-selected cadence at speed. I am using them about as much as the 12- and 13-tooth cogs on my old 2x setup (50/34 coupled to a 11–32 cassette), i. e. not too often. On the flats with favorable winds I was/am typically in my 50:15 = 3.33 or 50:14 = 3.85/42:13 = 3.23 or 42:12 = 3.50 — at a cadence of 100 rpm (my self-selected cadence at high rotational inertia/speed) that is about 50 km/h. I’m usually not that fast — or at least not that fast for long. 35–40 km/h is much more common, and I am more towards the middle of the cassette at those speeds.
When I was on Shimano 2x, I couldn’t quantify this, with SRAM AXS eTap, I fortunately can. According to the data I rarely use my 11-tooth cog, it is one of the least-used cogs. The 10-tooth cog sees much more use, because that is my overdrive gear (i. e. when going downhill). The same was true on 2x, I’d only use 50:11 on downhills and avoid 50:12. Even on a compact chainset, harder gearing was rarely called for. I had a loaner with a 52:11 top gear and there are two, three descents where I could make use of that extra gear — and in one case not for long as I can exceed the speeds of basically any gear on that descent (I managed 86 km/h once, but don’t feel like I need to do that very often).
Ditto with climbing gears: gear-wise I could have made do with a 11–28 or 11–30 cassette, but stuck to the 11–32, because I liked to cross chain and use 50:28 on occasion.
Feeling-wise, it does feel a little different with the smaller chainring, but that is hard to quantify. When I got my 1x11 hardtail, it initially came with a 30-tooth chainring, and that did not feel great in 30:11. I got a Rotor 34-tooth Q-ring on sale (for 30 €!), and that works much better. Although I still feel like I spin out too easily. The solution is obvious: get a 12-speed groupset. But I’ll have to hold off on that for a little while, my minister of finance wouldn’t like me chucking a perfectly functional 1x11 XTR groupset. 
I’ve been following this topic for a while now. And I think most of it comes down to “it depends”.
In my humble opinion when you live in an area with very steep climbs then maybe a 2x with a 11-32/50-34 would be better. In all other situations I would go 1x.
With a 12 or 13 speed and some good research about your cadence and power you can tackle everything with a 1x setup. You have the range and small steps required for flat, hills and even mountains. And drivetrain loss is relatively small with a clean (and waxed) chain (source: How Slow Are SRAM Chains and Other Drivetrain Efficiency Questions With Adam Kerin - YouTube).
And also as mentioned earlier, how much time do you spend in your 9/10/11 cogg? If you spend a lot of time there, you have the wrong gearing. The 80/20 rule applies here as well. 80% of the time you should spend somewhere in the middle of the cassette. The other 20% you should spent in the biggest or smallest cogs.
I use a 1x13 from Rotor with a 46 chainring and a 10-36 with a waxed Shimano XTR CN-M9100 12 speed chain for road as well as gravel. I live in an actuall somewhat hilly part of the Netherlands. And this combo is spot on for me (around 300watt ftp) for all the terrains I have nearby. For the flats at cruising speed (33kph) I sit spot on in the middle of my cassette (17 tooth cog). When going up or graveling I’m somewhere in my 19, 21, 24, 27 tooth cogs. Still a straight enough chainline.
And if I want to make it really exotic, I also have a 10-46 cassette when I go for some singletracks, Alps or very long gravel rides. For example Unbound 2023.
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Where’s that then?
I know, it’s hard to believe… I live in the central/east side of the Netherlands. The city of Apeldoorn region… Appearently some glaciers during the last ice age stowed (is that word?) the earths crust upwards.
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Yep, I’m a lower cadence rider - I like to be in the mid 80s when pushing on the flats at higher speeds so my preferred setup is 50/34 with an 11-32. My most common gears in this setup are right in the middle of the cassette according to the data from my etap.
VWA running 1x in MSR 
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SRAM. Couldnt afford a dropped chain with their atrocity of a Front Derailleur
And a 430wFTP helps eliminate equipment restrictions.
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1x with a chain catcher…
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If only WVA had read this thread first!!
Data point - first gravel race of the year for me today and I’d estimate 90% of the pointy end was on 1x and a surprising number running mullet eagle. Whether this is the result of bike industry conspiracy or it’s just a better system is certainly up for debate, but 1x has become the standard around here (central TX) for gravel racing. This was a rolling course, mix of smooth dirt, a little pavement, and lots of chunky gravel and without any steep or technical stuff (100k, ~3.5k of climbing).
BTW, it was an epic day for bike racing, perfect weather for this time of year. Another observation - gravel races are getting faster and faster every year as more of the strong roadies are doing them and pack/drafting dynamics are increasing. Winning speed of the race today was almost 22mph, 21mph last year, was only ~17-18mph back in 2018 and 2019 for this same race before gravel really started to explode. I wouldn’t attribute any of that speed increase to the move toward 1x drivetrains, but I also don’t think it’s slowing anyone down.
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This take is way too balanced haha.
I do think you make a great point about the changing nature of those racing.
