For someone like TJ Perkins, TNA was an upgrade. For someone like Punk or Edge, it would be a major step down. Those are two very different cases to look at.
The problem is all of this "career killer" talk is just pointless buzzword shit for a guy like Meltzer to throw around to try and degrade TNA, because for some reason he has a clear agenda against them.
There's lots of evidence of cases like TJ where being a part of TNA has upgraded their career, but no cases of TNA being a career killer.
Former big time WWE stars who have taken jobs working for TNA have had no problem getting cushy gigs back with WWE after they left TNA; look at Hogan, Foley, Booker, Nash, RVD, etc.
Former upper echelon TNA homegrown guys and/or high level indy talents who joined and later left TNA have had no problems re-entering the indie/International scene and doing well for themselves; look at Styles, Daniels, Kaz, The Bucks, Jay Lethal, Joey Ryan, Alex Shelley, etc.
The only guys who have really completely failed to do anything notable after having been pushed out the door by Impact, and appear to now have "dead" careers, are the guys who offer no value to anyone because they just aren't good and they never were any good whether they were with WWE or TNA, TNA is not responsible for the post-National wrestling scene failures of hacks like Morgan or The Pope. Hell, even plenty of former guys that the WWE gave up on and who had joined and had lackluster runs in TNA have still managed to continue on successfully after leaving both companies; look at Gallows or Chavo for example.
So, outside of Meltzer's head, where does this "Career Killer" narrative have any basis in reality?