And yet, also for a couple of decades or so, we could play video games that would function just fine offline and could online in multiplayer mode.

This take, and OP's, both feel like they're ignoring nearly half a century of how games have functioned in favor of the over-engineered industry of the past ~15 years. Again, as I said in my first response I'm maybe speaking out of ignorance here, but why are we acting like it's incredibly difficult to do something we were very capable of doing for a very long time, and for less effort than what we put in now?