Backwards compatibility is really only an issue for people who've been gaming longer than this generation and care about playing those games, and threw away there old systems, so its fairly niche. MS also brings a lot of their games to PC so its not really that much of a benefit, especially when older games on a newer console vs PC is skewed in PC's favor.
Especially when you consider the number and subset of games for backwards compatibility vs being on PC. It really doesn't do much for the question, why get an X1 if I have a PC. In contrast, I really want to play Melee since I've been out of of my dorm, and I defo can't play Splatoon or Smash 4 on PC.
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