Nobody should have to mindlessly grind out games to get to play a champion they already do well with.
And that's not even considering the sheer luck required to actually get m7. M7 effectively requires your team doing well, you doing very well, and the enemy team not surrendering. 6/2/7 200. That's the score you need on Ahri mid for an S (combined with frequent warding, good turret damage, and buying control wards, obviously). Most enemy teams surrender before then, or you don't do that well because a lane lost and you won't win as hard as you need to, meaning it can take ages to get m7, and it's almost entirely luck-based. And at that point you might as well fucking play Warframe or some other game you need 20 of a 1% droprate item.
And anything that limits picks effectively guts any trades in champ select...