I've recently tried syncing local content to my phone, but to find that content on the phone is difficult. The phone really wants to show me Apple Music stuff. I have to Library->Downloaded->Songs. Going to Artists or Albums just shows me "Download Music to Listen Offline". I really just don't want to spend the time I previously spent on my iTunes library all over again. I was really just trying to quick&dirty add content. They've made this unnecessarily difficult and I despise them for it.

Just go to the Library tab in the phone app. That's where your own stuff is located.

I have over 8000 songs synced to my phone, 100% from local files on my computer.

I never activate the "library sync" BS that Apple tries to force on you, because historically it has replaced your copies with incorrect or "remastered" (AKA dynamically compressed to hell) versions from Apple servers.

I've even caught it switching "library sync" on without permission during an update.