What makes you think if wow was sustained on "subs alone" they'd bother to make a better game? Subs are dropping steadily since end of wotlk / start of cata, who says they wouldn't at some point just shut down the game as unprofitable and swap their efforts into hearthstone, overwatch, diablo: immortal and whatever has bigger profit potential for lower development costs?
MMOs are outdated and the only ones rolling are the ones that live from mtx, even FF14 that has a sub as well has transmog mtx and whatnot.
You make some weird assumption that them making less profit would mobilize them do invest more? Why? If a product drops in profitability first thing you do is cut costs and second you put it in maintenance mode (= no new content, look diablo 3) or completely stop supporting it.
Plus literally you could say WOD had poor amount of content and was developed before tokens, and Legion launched after tokens were added and had much more content... is there a correlation? Well who knows except Blizz themselves.
People cry about store mounts in WOW but check any other MMO and it has 10x bigger cash shop. People cry about Allied Race unlocks but at least it's not SWTOR where you have to buy new races from the cash shop.
And thanks to people like you I can play wow for free. We can say it's transfering money from the rich to the poor.