> First and most importantly, ads were still being served via the stream; it was just happening via whatever third-party client the user was using. The main difference here is the app being used, and honestly, is that really such a bad thing?
From their perspective, they likely thought so. The amount of user tracking and spying data they can hoover up via an app., which is not available to them from someone using VLC (or another player) is huge, and it is very likely that a huge part of their monetization of Pluto TV streams comes from the tracking data they can hoover up via their app.
No app., no tracking data, no tracking data means lost profits from selling the same. So of course they try to abuse the DMCA as best they can to claw back those lost profits.