Don’t know if you solved your issues, but regarding your plugin list:
FabFilter - never have any performance issues
iZotope - sometimes heavy, mainly if the plugin is visible so not so much an audio processing problem as much a visual rendering deficiency
Valhalla - never have any performance issues
Waves - never have any performance issues, but don’t use them much these days.
Klangheim - I have noticed that for some reason, at least on my system, MJUC is far heavier on the CPU in Nuendo and Cubase than it is say, in Ableton. And when I say heavy, I mean 7 instances of MJUC bringing down an i9 7940x.