> Just try to implement, for example, a hexagon-based isometric game. There are no off-the-shelf implementations -- you'll need to redo the pan / zoom / click controls yourself, you'll need to implement the pathfinding, map layers, interface state machine etc etc etc

Sure there's off the shelf implementations.

Off the top of my head I would suggest starting with evaluating godot 4.

They have isometric view, pathfinding, and all of the rest you are mentioning.

Sure they do -- but once you introduce at least one custom component (i.e. hexagon map), it's actually not straightforward, how to integrate it with the rest of the controls.

I can't say whether it's me who's stupid, or it's just not very easy to make good UI in game engines. I don't say that's not doable of course -- i'm just saying one would need to invest quite a bit of time to work out how to do this.