Last.fm isn't really expanding their API unfortunately. You can however see Last.fm stats in the main artist/album/track commands.
As for spammyness, I'm aware this is an issue. For non-bot channels I recommend using .togglecommand and enabling just a few specific commands, and setting a small embed mode so .fm commands don't take up too much space in chat.
Yeah, this seems to be the case for a lot of people. I frequently get support tickets asking how to connect Apple Music. There are some alternative players you can use, but it's not really an accessible solution suitable for mainstream use
These integrations are lacking compared to Spotify. For example in Tidal you have to set it for each device where you install the app, and it doesn't work with things like casting. It's easy to forget to set it up which can cause gaps in your history.
The Plex integration gets pretty close to native, but it only scrobbles after a track is done, it doesn't have 'Now Playing' support.
As for Deezer and Quobuz I'm not sure. Afaik Spotify still stands alone by being set-and-forget, working on any device and having full feature support.
Last.fm is still used quite a bit, mainly as a listening history tracker rather than a radio or recommendation engine.
Spotify is still the only big streaming service with native platform-level scrobbling. For everything else it's a lot more DIY, usually with third party tools at the device level.
A big reason it’s still relevant is the ecosystem around it. The API hasn't really changed in 15 years, which makes it easy to build tools where a username alone is enough. That kind of lightweight social integration has mostly disappeared elsewhere.
Today, the social / community side is almost entirely just Discord. Nearly every music related server has a bot that displays Last.fm stats. My estimate is that abut 10% of Last.fm their users are also active in Discord music communities.
(Disclaimer: I run .fmbot, a Discord bot that integrates with Last.fm.)
Can't wait to try out GPT 5.6 at some point when it comes available.