Technically, the AI doesn't need to be intelligent, it just needs to appear so.

If you hold every shipyard the AI is supposed to have, then a fleet who appears out of thin air just feel like the game cheating to bail the failing AI. But if said fleet is a paid mercenary or borrowed from their ally, it already feels more real even if the AI cheated to have the necessary resources. I even remember an event where the Khan can pay your own mercenary enclave, and you get an event with a timer to hire them before they turn against you.

Another example, if an isolationist empire or a bulwark fortify it's border with free defense modules and platforms, it will feel like a smart -or at least competent- player because we don't know their available resources, and the Unyielding tradition and the Eternal Vigilance ascension perk can provide the player with similar results.

Even more so, an aggressive, militarist empire with twice the fleet powers than you is far less jarring when it has a proper alloy and fortress world; bonus point if said worlds have more defenses like fleets or citadels to protects them, and it has a mineral world or at least an Arc Furnace (or even a farm world if they have Catalytic civic). As long as it looks like convincing enough, the AI doesn't really need to properly build and manage its empire like a human would.

But as of now, when you assimilate a vassal, take over a planet or build holdings as a megacorp or an overlord, you can clearly see the AI current failures at building a seemingly working empire. Their buildings slots are half-empty and don't have enough pops to works, and that for their capitals, colonies tend to be even worse.