The AI will just use it's native MaA, while the player can customise their culture to have all the best MaA.
The "best" MAA are about 1/100 as impactful as average MAAs with the current insane bonus system
Even if your entire roster is, somehow, composed of nothing except horse archers, or elephant riders, or whatever, they still couldn't face a fraction of the size of this army that was completely crushed in this example:
Levies are basically worthless. Despite being presented as an entire half of the tax system and an entire branch of your army, levies are only even worth raising as a duke/count and for bolstering your numbers for raiding/siege purposes. After...
forum.paradoxplaza.com
The fact regular MAA can surpass 200~500 damage each, with just the nomad building and accolade upgrades cripples the game beyond any hope of repair, specially when you consider the hidden combat width system, these guys are just instantly wiping any front the enemy puts against them instantly. There is no real battle going on.
Specially when I'm forced to create a large army of soldiers with varying unit types from vassal levies too, and I'm forced to field a much larger army, subject to combat width, against a much stronger enemy army since the enemies also wouldn't be using the trash "levy" unit type either.
No matter the scenario we come up with it couldn't be anywhere as ridiculous as those screenshots
I don't believe there should be any +damage or toughness boosts for MAA anywhere in the game, that includes buildings and accolades, maybe a flat boost in quality after you unlock each research era, but a tiny one, roll back from the stacking +90% boosts to something like 5% or 10% in total, like EU4 does things.