Anyone can install a different keyboard with its own emoji pack no?

Emojis are part of font packs which are pretty standard and open via Open TrueType, no? Apple isn’t quite as simple to do that with (albeit possible via 3p keyboards, custom per-app fonts, or custom device profiles), but it still feels like I’m not understanding your complaint.

The problem is that the receiver will see a different version of the emoji (or perhaps they don't even have the particular emoji installed).

Which has always been the case for fonts. Just because I write a letter ‘T’, there’s no guarantee how you’ll see it. It’ll look very different in Windings.

Yes. But just because it's a problem for fonts doesn't mean we should have the same problem for emoji. If you don't care if emoji look different, then that's ok, but please don't blame me for caring about their exact appearance.

Which is fair but you can't have "the one true rendering of emojis" and also have "people/platforms can use different emoji packs if they want." Someone who uses a different pack than you might have a different intention as a sender and as a receiver your message to them might be misinterpreted.

I think "federalized" is the term you're looking for.