Typically, these sorts of mechanics are
less bad in commander, just because... well, it's all relative, right? And commander has all sorts of crazy stuff flying around. Also, people kind of have to pack removal (of all types) in EDH because you can't expect just to win with a dumb aggro deck that can't actually interact with a lot of stuff, and board wipes happen, and you're facing multiple foes. Thus, there are just a lot more chances for you to face the right sorts of answers for whatever silly thing you're doing.
(For comparison, Fynn was obnoxious in Standard, and I suspect that the likes of
Venerated Rotpriest will be, too)
Also, "underpowered" and "archenemy" are not mutually exclusive! Infect is perhaps underpowered in part
because it's so often the archenemy, because it's widely hated. Or,
consider "kill on sight" commanders like Tegrid - these are powerful
if left unchecked, so they're not left unchecked; overall, they're often not overpowered at all, but they have the potential to get out of hand if they're not targeted.
Anyway, to come back to the question... in general, I am not actually that keen on this kind of alternative wincon. I find them often to be... sort of parasitic? For a start, poison and mill don't really do anything unless they do everything; in a multiplayer game especially you can't exactly combine forces with anyone. Conversely, they subvert the expectations of the game and are hard to combat. We rightfully expect that our life total is important, but no matter the number of blockers we have or the board state we create or the card advantage we might have, we can still lose to poison counters or decking out. Infect is actually better in this respect because it's on creatures that have to hit you, but ETB poison + proliferate is rather horrid this way since it can at times be impossible to deal with short of player removal.
It can be healthy to have alternative wincons, to stop lifegain being too annoying, or to keep the game fresh - but when they're not really designed in from the start, they can feel... well, that's why I say "parasitic" (not just because of Phyrexia and parasites).
Toxic feels like an effort to make a better-balanced, "fair" version of poison. It sort of limits the amount of poison you can inflict per turn, and it also doesn't stop you from lowering life totals at the same time. Corrupted is a way to get payoffs before you hit 10 counters so it's not so all-or-nothing. They also seem to have added a bunch of noncombat ways to give people poison counters and some way more pushed proliferate, so I'm not sure what they are on or how that will pan out, but it may work.