"co-host would be better if they added ActivityPub support"
Some people really don't get it huh?
Yes there is very much a use for spaces ala mastodon, the whole point is that cohost isn't a replacement for birdsite, it's way different in ways that are supposed to help make it a better place to actually exist in and not turn into engagement chasing. And SVGs won't render on other sites anyway so who cares.
There's upsides and downsides to both, and one or the other may be a better option for you, but they're just very different places. It's kinda surprising to see people so locked into the mindset of "the one true option" and that anything they use instead of birdsite having to function like birdsite, or at least have everyone in the same website.