Aegi on stall is ****. Did you even play on the suspect ladder? It was so bad I had to stop playing for a while because it was ****ing terrible. The meta now isn't cancer (minus thundy cuz he's broken af). It was cancer on the suspect ladder. Idk why people ***** so much about XY OU. Except for Thundy, it's fairly balanced.
So what if its easy to put a mon on a team? You see Garchomp everywhere. You see Xard everywhere. Last gen had Scizor, Jirachi, and Keldeo. Gen 4 was Rotom and Scizor post Platinum. Gen 3 saw Metagross, Swampert, Blissey, and Salamence everywhere. There will always be mons that are easy to fit on teams no matter what you do. If they're not broken, which you admitted Aegi wasn't, then there's no reason to ban said mon.
What exactly would the meta shift to? If anything, genie and Birdspam gets better, and you know how much everyone hates those. Maybe Bisharp will decline in usage (I personally don't see that happening). Maybe Garde and Medi will take OU by storm. This is all theoretical. I don't see the problem.