I'm not going to say I "trivialized" this mission but after a while I got the right setup and then the mission kind of became smooth sailing. Not too proud of it since I DID abuse pauses.
>Get 5 TCs, all relevant techs and a sprawling horizontal line of outposts across all 3 bases
>Minimum 50 farms before battle begins, 70 is fine, 90 is ideal
>Open with +50 fully upgraded elite companions when the battle begins, follow it with phalangite spam from +15 barracks
>Deploy archers for Perdiccas and skirmishers for Parmenion as soon as possible, it will hard shut down the first waves, allowing to preserve your momentum
>Once nearing 250/300 pop with 7 TCs and a stable economy, get 15 stables and start teching into Royal cavalry
>Spam Royal cavalry, keep your allies together and win
I cannot overstate how useful that skirmisher and archer support are for your allies, and while companion cavalry are amazing, they produce too slowly from 1 castle, it's better to have 80 paladins than 30 companions