This part is trivial nowadays: sonarr/radarr and related handle discovery and library management, and jellyfin does the playback.
Reasons I got back into piracy included trying to watch a series with my wife, and finding it gone. Seasons missing while streaming, UI becoming worse (for the last few years of Netflix I fully relied on an external paid service to discover new things on Netflix because of that). More and more content I cared about being removed, with lots of content I don't care about getting added - while price kept going up _and_ account sharing policies being put in that'd match my non-account sharing use case.
I'm still paying for Disney+ - though based on the Netflix experience I'm adding everything I'm interested in to my local library.
Amazon Prime got kicked out after they got too expensive - and even while I had prime I never actually used the video player as the UI is so horrible, but already back then pirated all the stuff I was paying for.