Ooh, yes for for this case, the LGPL would be a good middle-ground for OP's concerns.

do mind that (and i'm pretty sure this still works with AGPL but this isn't gospel) you can have the engine be open source while keeping the assets proprietary and requiring they be purchased to actually sensibly play the game.

This is how the original DOOM works, there's an ocean of modified doom engines but you still have to buy the assets to play the proper actual DOOM game. You can use alternative asset packs but it'll look and sound like a fairly different game.
And of course it's vastly easier to create alternative assets for such a simple game, compared to the labour that would be involved in a larger modern game.

That was a frustrating read. Dude gets screwed by Microsoft who effectively steals his code and rebrands it as theirs and then he goes on to talk about why he prefers MIT.

That's understandable, though one of the other commenters suggested the LGPL which might make for a good fit for your case. Here's a comparison with the other two if you're interested.

The AGPL is just the GPL with extra rules requiring sharing the code even if you expose it exclusively via a service.

AGPL is GPL + network services protection (preventing someone taking your code and spinning up a for-profit selling services without contribution back). If you don't care about people stealing your code, closing it, and selling services based on it, then there is no need to consider strict copyleft licenses.