IMO rts don’t need good AIs because if you want a challenge you can just go into ranked multiplayer.
Singleplayer strategy games on the other hand, like Total War games, Paradox games or Civ games would benefit from a truly competent AI (and that’s why Sid Meier is full of shit, his point about an AI being too good stands for 1v1 games, but not HIS games). Also keep in mind that in these games, the player is just one faction among many AIs, and these AIs fight eachother as much as they fight the player (or at least they should).