I don't think it's a problem that they're against federation. I think federation is nice, but it has some clear trade-offs, and I don't feel like it's something Signal needs.
I don't even think they have to officially support third party clients or provide a stable API. I'd have no problem if they just occasionally made API changes which broke unofficial clients until their developers updated them.
But I really don't like that they're so openly hostile to the idea of other people "using their servers for free", with the threat of technical blocks and legal action which that implies. Especially not when their official client is as bad as it is. (Again, it's fucking blurry!)
I don't even think they have to officially support third party clients or provide a stable API. I'd have no problem if they just occasionally made API changes which broke unofficial clients until their developers updated them.
But I really don't like that they're so openly hostile to the idea of other people "using their servers for free", with the threat of technical blocks and legal action which that implies. Especially not when their official client is as bad as it is. (Again, it's fucking blurry!)