And no, they don’t speak to one another / find one another or are able to follow / like / reply to one another as one is told the Fediverse works.
This is true, it is a problem, but maybe not as big a problem as you think.
Kbin combines the data model of both Lemmy and Mastodon so Kbin can interact with both of them perfectly. Mastodon can interact in a limited way with Lemmy. Frendica and Pixelfed also work fairly well with Mastodon, so Kbin should be able to interact with both of those as well, although I have never tried. PeerTube is probably the least compatible, although I can upvote and post comments on PeerTube videos using my Mastodon account, and follow PeerTube accounts on Mastodon. But I can't create new PeerTube posts on Mastodon. I hope in time all of these different app services will be able to interact with each other more.
The most difficult thing right now is moderation tools. Right now, banning instances is very coarse, and it also deletes the entire social graph between instances, so people who were following each other lose their connections with each other, even after the ban is removed.
There are people working on solving that problem right now, but it might be a little while before the changes are spread throughout the network.
What I would like most is if I can create one ActivityPub account and use it on every ActivityPub service. This for me would be a perfect solution, because then I could use any app using a single account. I would also like to see it possible to ban instances temporarily without losing social connectivity, and I would like to see better moderation tools for individual user accounts being banned by an instance.