Games

This has been discussed a lot over the decades (with some VERY good articles written by assholes we try to pretend don't exist))

The gist of it is: AI cheats because the alternative isn't "fun" and rapidly outpaces humans.

Because in an RTS? After you get a build order down, the big decider is Actions Per Minute (APM). From a build standpoint, it is the idea of triggering the appropriate research the absolute second you have enough minerals. From a combat standpoint, it is rapidly issuing move and attack orders so that you always win the combat triangle. The former isn't significantly different than just having cheaper research or faster build times. The latter is actively demoralizing in the same way that we all died inside when we first got permission to go online in Starcraft. Except at a level that even the good players realize they ain't shit.

For grand strategy games (barring real-ish time ones like Stellaris) you basically have two real approaches. The first is the games with research options (... like Stellaris. Look, I have been playing a lot of Stellaris lately). We try not to acknowledge it but RNG has a massive impact on that when you really want to get torpedoes but no options are popping so you are just doing the fastest research choices you can to get a new pool. And the difficulty option there is... a known order.

The other are the very elaborate fixed tech trees. Obviously this gets back to build order. And the reality is... the benefit gained from rapidly updating the hard mode AI to use the current meta just isn't worth it. That IS somewhere that an optimizing function can be applied to (and... semi-off-the-record but that has been a thing for over a decade and is why devs aren't THAT surprised when a "new" meta takes over in a strategy game) but it becomes a question of how much it is worth it.

All that said, we are seeing a lot more effort put into "learning" AI in racing games (driveatars) and fighting games because those tend to be cases where even the best AI is still expected to be "human" and we aren't TOO demoralized when we realize we are in a pub with Daigo. That said... there is a reason that modern SNK Bosses tend to have super armor rather than frame perfect inputs. Because the former is "bullshit" but the latter is just mean.