I'm not sure exactly what you expect of him?

It's not a tantrum, just a statement of limitation. The primary reason for Bazzite to exist is to have a SteamOS-like Fedora. He mentions, in depth, how the 'simple' answer about using flatpak doesn't work, because flatpak imposes isolation in ways that are incompatible with the use case.

His options seem to be to be "polite" and quiet right up until the change gets approved and implemented and only then yank the rug out from his community, or make the broader community know the implications of removed 32-bit userspace support.

This seems to be the whole point of soliciting feedback, to know what you are likely to break. It would be supremely odd if you make a proposal, solicit feedback, and call any mention of a bad consequence a 'tantrum' when that was the whole point of framing it as a proposal.

Seems like he needs either Steam to go 64-bit or for Fedora to keep 32-bit since flatpak can't help and, presumably, he doesn't want to try to take on the maintenance burden of trying to carry forward Fedora's 32-bit rpms for the same reason Fedora is trying to get out of carrying them forward. Assuming the broad community decides Fedora 32-bit userspace is still needed, then it's far less incremental work for Fedora to maintain along 64-bit than it is to independently add it back.