There have been a bunch of studies trying to evaluate something as ostensibly 'simple' as how complex a position is. And they're all terrible. It turns out that what's complex for a human is extremely difficult to define, because we can find very simple positions extremely complex (R+B v R for instance) and some very complex positions are very simple because correct plans are 'obvious'. Similarly some quiet positions can be very complex when it's difficult to find the correct plan.

And all of this also changes with level. I'm speaking of correct plans, drawing a technically drawn ending, and so on. If a player is weaker then complex for them might simply mean when there's lots of pieces doing lots of stuff, making them more likely to hang material to a simple threat. And the aforementioned RB v R ending might be trivial for them ( on the R side) because their opponents are not going to be strong enough to create plans that can apply pressure and try to make progress. They're just going to move their extra piece around hoping you blunder something.

So getting back to engine strength - I think figuring out what's complex for a human is a very basic prerequisite, amongst several, to making an engine that plays human-like. And we're just not there yet, or seemingly even especially close.