@Jacob Lewis You put it much better than I did. Thank you.
I will also expand that a more common problem is how a system handles "scaling" or "power levels". Which might be touching on the long term progression that the OP (
@Elvish Lore ) was trying to address, as the high-end is the more common breaking point. The DnD family is notoriously wonky at extremely high-levels, system-wise. There are other systems that are worse. There are even some systems that invert that (the original MEGS version of DC Heroes from the 80s).
But as you rightly pointed out, all of these are a question of pacing and taste. Both of the GM and the players. If your players enjoy the wonkiness, then go ahead play DnD 3.x in Epic Levels. But you can still have an enjoyable, multi-year (60+ session) campaign in DnD 3.x without ever reaching Epic.
Perhaps a better question for Elvish Lore's purpose is "What game systems are not suitable for long-term play? (Given this definition of long-term play.)"
One that's been touch on already is Pendragon, as it fully expects any individual player character to be retired over a long-term campaign. It's still a VERY solid system, and if you relax the "must be the identical character through the entire campaign" restriction, is still immensely suited for a long-term game.
Another would, in my opinion, be Paranoia. Again you run into the identical "same character" issue, cranked up (as your original character isn't even expected to survive the first session). I, personally, would also have a very hard time sustaining Paranoia's tone over a long-term campaign. I find it a game for conventions, however. And I can imagine a GM that
could manage a long-term Paranoia campaign. (It's just not me.)
But even with inverting the focus, I'm not sure there's any meaningful results out of the filter. There's just too many TTRPGs out there.
Which brings it back around to your final point. Pick the system you and your players like, and just go for it.