There’s a lot of audio tools I don’t use, so what are you missing in terms of audio for linux? Personally, I wouldn’t use any other OS for audio right now.
I agree it can be hard to set up a reliable audio-capable linux, but since you have been using it for 10 years, that shouldn’t be a problem for you.
Another problem I can agree about is the lack of a multitracker with very good editing capabilities. Ardour is a superb daw for recording and playback, and I would say its is a sober alternative to protools, but I lack some convenient editing features in it.
Regarding plugins, there are hundreds of ladspa plugins, and many of them are really great. If you trust your ears, you don’t need to pay a lot of money (or download cracks of expensive software) to feel safe that your plugins are of high quality.
Regarding mastering tool, have you looked at jamin?