Doubles are heavier? A shifter, a length of wire, a small chainring and a derailleur weighs how much?
Depends on the components but
XT shifter 130g
XT mech 150g
XT 22T chainring 20g
4 chainring bolts about 10g
40g or so of cables
42T chainring adds about 50g to your cassette, and you need to add a couple of links
So all in all, about 300g of weight saving. But that’s just one benefit, you get better chain retention, better mud manners (surprising how much difference this makes), and no recovery shifts from going up/down front rings. None of these are things you need to be a pro to benefit from.
The tradeoff of ratios is far less than most people realise because so many of the ratios you “lose” are just duplication. (the exact same was true when people started to move away from triples for mtbs)
It’s not for everyone but it’s definitely a good option for a lot of people. If you’re not fit enough, or you like a close ratio cassette then obviously look elsewhere. All my bikes are 1×10 just now, I built my xc bike with 2×10, rode if for a little while and that just confirmed to me that I’m right to stick with 1×10.