Conquistador de pan
Where did you hear anything like that?
This thread, actually.
- Fire, 8 (including Primal Groudon)
It doesn't need to Dynamax to invalidate nearly half the Pokemon in the game. In fact, special Dynamaxers are less viable simply for Chansey existing as it can force most of them out (or simply stall them out) if they Dynamax while it's still alive. However, there is another factor that I realized I hadn't considered, which I'll touch on in a sec...It doesn't really benefit itself from dynamaxing though. All status moves become Max Guard, and it lacks the power to make much use of attacks that use attacking stats.
Assuming Toxic doesn’t becoming a Move Tutor Move it will be heavily nerfed (at least in formats that require Pokémon obtained in Galar) as the move is its main means of racking up damage (aside from Seismic Toss). It could get it as an Egg Move but all the Toxic users in Gen 8 are either Poison-types or based off things themed around Poison (bar Bellossom but only because it evolves from Gloom).
Well, ignoring the fact that Home will likely allow you to transfer a Toxic Chansey from a Gen 7 game (unless for some reason checks are in place to prevent such a thing), Chansey doesn't actually need Toxic to 1v1 nearly any special attacker in the game. Even in Gen 7 where Toxic Chansey was perfectly legal, it would sometimes drop it for Thunder Wave or Wish + Protect (which admittedly isn't feasible on carts thanks to Wish Chansey coming from an obscure Gen 3 event, meaning legitimate Wish Chanseys are nearly impossible to find). Gengar can now reliably break past Chansey thanks to +2 Life Orb Focus Blast 2HKOing but it already beat Chansey to begin with by Taunting it. Just about every other special attacker is susceptible to Seismic Toss, and even ones with recovery can generally be PP stalled if Chansey is carrying Rocks or another high PP move instead of Heal Bell.
That being said, like I mentioned earlier there's a factor I didn't consider; Softboiled isn't in SS. Unless the expansion pass reintroduces it (and I don't necessarily think that's out of the question), the Chansey family won't really be viable unless you can track down one of those rare Wish Chanseys as they'll lack any reliable means of recovery outside of Rest and possibly Life Dew. Rest Chansey could be somewhat usable thanks to Natural Cure but will definitely lack the stalling power of Softboiled sets, especially without access to Toxic.