Yeah, I faced the same conundrum back in the Radeon VII/5700XT days. I had gone with a Radeon VII and a 5700XT, believing AMD to eventually support the latter in ML.

Using the Radeon VII for ML was still pain, but I had more free time back then and was willing to tolerate the tinkering. The support for the 5700XT never came, was just constantly led on by AMD devs on their GitHub.

I didn't really have that kind of free time when I wanted to upgrade, so buying 3090s ended up being the only realistic option. Even on Linux, as long as I'm not trying to stick to the latest bleeding edge kernel, the closed source drivers work very well. Thus far I feel the 3090s have been well worth the extra cost simply in terms of tinkering time saved.