One by is really simple and works great on my gravel bike - BUT - when running smaller rings in front for easier climbing you do spin out on faster sections. I ran a 26 front ring at Rasputista gravel race two years ago and climbed everything except some deep mud and snowy sections in Cyberia - unplowed keep Road in April in Vermont.
I am a back of pack rider but passed a lot of people on climbs but when it got fast the folks with higher gearing repassed me and left me in the dust but I would catch up again on extended steep climbs - I probably could have kept up better with a 2x.
But in hindsight I wonder if using a bigger ring for more speed and just dismounting and walking on the 17% grade sections would have given my legs a rest. It was funny cause could see people walking and slowly catching them but took several minutes to close 100 yards - wonder if I got off and walked if my leg muscles would have been fresher and able to charge harder on flats afterwards.
****** One thing I run into with 1X in Zwift often can’t peddle fast enough on fast downhills to keep up and power goes to zero because can’t get cassette turning fast enough with small ring in front to keep pressure/power on trainer.
But salsa Cutthroat with 10-42 sram rear cassette and 26 or 28 front ring makes climbing mountains like Cadillac Mountain super easy - can climb with normal cadence and still keep watts quite low like easy L2 power zone.
This makes great recovery ride bike even in very hilly terrain cause it is geared so low you can spin up hills vs muscling up.
I love my geared Down bike - finished Rasputista 4000 plus feet climbing and my legs weren’t toast at all - but you do end up watching the other riders dissappear on anything past 18 - 21 mph sections cause you are spun out at 100 plus rpm - but you can climb like a goat all day and not feel it.
With 2x if you can get gearing low enough to climb effortlessly then can have 10-16 more teeth on front ring when you shift not to get left in dust when pace picks up.
(My cutthroat has 1x11 mountain bike cranks so can run 24 or 26 ring up to 40 something ring - just have to change your gearing/ring to match terrain you are riding - 1 have force one model two years old and cranks are sram MTb cranks - have to check cranks on other builds of cutthroat as run mtb cranks limited to like 30 or 32 for smallest ring - so would have to change cranks to get super low gearing I am using in mountains)
I also have 1X on Fatbike run 26 tooth front ring for hills in snow - works great on climbs but my friends with 2x can shift to big ring on faster trails and once I spin out they ride away from me - but I get good high cadence drills peddling 110-12- rpm trying to keep up.