I think the reason why SRAM set the chainline at 49mm is because so that you can run larger chainrings. I know on some frames, a 34T is the largest you can run up front. You can tell the chainline may not be "optimal" is because when you back pedal in the 42T...the chain will drop off onto the 36T. I have a XX1 crank and when I'm in the 36 and 42...I can hear that my drivetrain makes more noise. That is a big reason why 1x chainrings wear so fast. If you look at the majority of worn 1x chainrings, its the outer teeth that gets worn out first. People are getting as little as 400km's out of their XX1 rings before they start making the dreaded grinding sound.
Garabruk makes direct mount rings that set your chainline at a 47.5mm chainline. I may try one of those. OneUp's chainrings come with 2mm chainring spacers to help you dial in your chainline.
Compromise is part of the 1x game. You either lose the top or bottom end of your drivetrain. I run a 30T with a 11-42 cassette...and I rarely run out of top end. It all depends on where you ride. I find that gearing is just as personal as any other part of the bike. What works for you does not mean that it will work for someone else. I would rather sacrifice the high end when I could just coast than push up a hill because I wanted that high gear for that 10% chance where I might use it.
I don't ride my mountain bike on the road. I have a road bike for that.
