Just in the process of going the opposite way, but for reasons a bit convoluted.
For me 1×10 is a pretty much perfect offroad solution. There are some caveats though. I was running an 11-36 cassette (only point in going 10 speed otherwise stick with 9 in all honesty) and for a while ran a 36T ring, then a 32T ring. The 36 was perfect for almost everything except steep/long climbs. The 32 was perfect for just about all offroad but spins out too quickly if you have to go on road at all. The other problem is that riding with a single ring, your pace is dedicated by your setup, not you. I’m actually quicker on a single ring setup than I was with a double or a triple, cos I’ve got no option than to grind it out on the climbs. If that’s suits then its brilliant, and it does teach you to MTFU a little.
However. If you ride in social paced groups a lot, you’ll find that it can be a PITA. If you’re ever stuck behind anyone twiddling their granny ring and you can’t get past, you’ll go from being a reasonable human being, to a seething mess in moments, cos you simply can’t go as slowly as they can up hills!
If you want to go quicker, want a simpler setup, want to become smoother and learn to pedal better/more efficiently, get a single ring setup, particularly if your rides are fairly short, sharp affairs. If you’re into all day epics, or slow paced social rides, 2 or more chainrings will always make more sense.
As for me, my GF has just started riding, and it makes more sense for me to have a setup I can ride along at the same pace as her with when I want to, but still have the gears that are optimal for me going quick when I want to. To that ends I’m fitting a 24/36/Bash setup with 11-36 cassette to my hardtail (same as on my full sus) as for most of the time I’ll never use the 24T as the 36 is ideal, but if I want to sit and twiddle up a hill with her I can do.