Totally missed that part. That is nuts. Thanks

How does this differ from a forced Microsoft login in eg. Forza Horizon 4 or Halo?

Forza Horizon 4 currently

I tried the Epic Version of BL3 (when they gave it away) via Heroic Launcher and that works flawlessly. However I did not yet try online coop.

This is the correct thing to do when it breaks, recompile and link against the new libs. Otherwise you could see funny behaviour.

I am playing my epic games exclusively via heroic and it is a blast.

Played it for the first time some weeks ago. It was like playing Half-Life 2 for the first time again. Loved it.