Zed audio is definitely in the High end bracket, their amps are insane.
I'd say Sundown has moved up a bit from the other similar companies with their new amps and the newest sub lines like the X series, I'd put them around Mid-High end, same with Arc.
Fi seems to just be a middle of the road company, along with SSA.
Pioneer and Alpine are at the lower end of the middle, most of their equipment is decent, a few really low end products, and a few really high end.
Audiopipe is barely above flea market. mostly junk with a few good ones.
Ultra high is reserved for companies like Mosconi, Gladen etc. That only put their name on the best possible products.