I don't really understand the hate for it - it works really well for me. Enables me to upload all my custom songs and unreleased stuff to my Apple Music library and have them side by side with music in the Apple Music catalog.
The only thing I find a bit janky is the search when it doesn't very efficently swap between searching your own library or searching Apple Music. It can be clunky to switch and sometimes you get stuck levels deep and have to delete the search and start again, it needs work here - maybe use some AI to decide if it should search your own library or the AM one! Two search boxes seems a mess, I don't know the best way to do it - someone must be able to figure it out though.
Yeah it's exactly that, search. I have it set to show the iTunes store aswell because I still buy albums occasionally, it's even worse with three tabs.