The game was dead as soon as AE was released. As a vet of CoH who remembered it taking months it seemed to reach one toon to lvl 30... getting to lvl 50 in nearly one day thanks to AE was an absolute joke. Back in the day getting your travel power at lvl 14 was "gratz" worthy. Circa 2012 COH such accomplishments compared to then are laughable.
MMO's getting "easier" and "sleazier" is not unique to COH however. This fact, combined with players blatantly cheating on most MMO's by buying currency, accounts, and levels has pretty much made me lose interest in just about ALL MMO'S. COH was not an exception to this. Ironically enough, AE indirectly was the light that illuminated me to the world of "pay to win" mmo gaming.
It is a shame that it seemed to get a bit too easy.
But I don't follow the mindset that "AE ruined the game". If someone gets to level 50 in AE, while I'm running missions and never seeing them play, how does their existence, subscription (or microtransactions), character, or playing time in any way affect mine? The only two ways I can think of is that they're also buying things on the market... but by that argument, they're as likely to be selling things on the market, thus having no net effect... and that the money that they spend on subscription and/or microtransactions supports the game so it's less likely to close.
So, in the end, while I do wish the game remained a bit harder in general, that's something completely separate from saying that a portion of the game ruined it for others. Power leveling, AE, power-supergroups running all-Rad teams, Hamidon Raids, PvP, Incarnate Trials, whatever.... Sewer Trials back in the day, again, whatever. They're all good, as long as they all keep some additional type of players interested in the game.