"In the grand scheme, this is a minor change that brings Google Messages
in line with other chat apps."
Well, if they're duplicating what other apps already do, you're screwed
unless those other chat apps give you more granular control, like
options that apply only within scope of the app where you could disable
animation just for that app.
My reading of the Google announcement was the emoji was animated only if
it was the only emoji in the message. One emoji: animated. Two, or
more, emojis: no animation. So, I suppose a workaround would be to put
2 emojis in the message, like 2 side-by-side frown faces to show you're
doubly sad. Alas, you can't make senders use 2+ emojis as a workaround.
I found a Youtube video on how to disable animated emojis in Telegram,
but, shit, was it a convoluted method.
https://www.youtube.com/watch?v=LMhAzWC_Ft8
WhatsApp may not have animated emojis, but they're planning to.
https://wabetainfo.com/whatsapp-is-working-on-animated-emojis-feature-with-lottie-to-enhance-user-messaging-experience/
Reminds of users that flocked to Incredimail (akd IncrediMal, thankfully
died March 2020), because they wanted to bloat their messages with fluff
instead of revealing their low content.
As you said, disabling animated emojis in Google's Messages app requires
disabling animation everywhere. You're not alone in wanting to have
simple and clear communication without a bunch of childish cutesy crap
foisted on you. I consider inane the use of emojis. Too bad the chat
apps don't have an option to filter them out, like "Adult mode".