I managed to gear my druid to heroic iLVL in like 2 weeks without doing a raid or M+. The problem as I have said many times is not the amount of loot that drops, it’s the many various sources of gear. To be able to get to heroic iLVL without going the traditional dungeon > raid is utterly disgusting, sure too much gear drops from an M15 if you time it well enough.
But than at the other end of the scale if you run a low untimed key you only get 2 pieces which I think is a plenty. They should never drop more than 2, timing the key is already a bonus in itself with a new key being provided at a higher level and therefore a chance to get better gear.
But one piece from an M0 through to an M20? This will mean some players will just stop doing higher keys than what the maximum iLVL drops are plus one, meaning currently some players will do M16 at best in case they fail the time, they will still than have an M15 to spare.