When playing the mod with high difficulties with cheats for the AI i found its best to rush engineering and keep the barracks while waiting 10-20 turns before committing to the hybrid inf. As for what you could do until you get to that point

For chaos factions shielded spearmen with the new cannon spam works best giving you a disposable shielded front line and cannons to delete their superior melee units before they get to you. I also recommend large gaps between your spearmen and your artillery units( dont forget pyre hulks to protect your arty)

For vampires/tomb kings, shielded inf, pyre hulks and arbalests work best. The pyre hulks are the glue to any empire frontline and when mixed with any infantry unit they become 1000% more effective. In my experience fell bats, dire wolves and other entities are too overwhelming for tier 1 hybrid inf

for wood elves i recommend rushing cinder wind calvary, cannons and some anti large pyrehulks
the cinderwind calvary are great for slowing skirmishing units while your cannons pick em off

For skaven pyre hulks and tier 1 fumecorps handgunners hybrid inf with some cinderwind calvary if possible. Fume corps handgunners really excell at trading at about 2 or 3 to 1 with skaven chaff in a checkerboard formation despite having a relatively low upkeep cost. The best faction to build hybrid early against

Lizard men are a nighhtmare for hybrid inf and i currently just recommend cannons and anti large and pray you can kill the chunky saurus boys and jurassic nightmares before they hit your frontline

Also imo having a celestial or fire wizard is critical for buffing and supporting hybrid inf should you rush hybrid inf anyways. Another thing to note is that your tier 2 hyrbid inf which are the meaty part of the mod require 2 turns to recruit so a pre-emptively built stable to increase recruitment limit can help mitigate the head ache of trying to get a viable full hybrid army built. Also if your gonna play karl i highly recommend not being stubborn and still leaning into his elector count troops and calvary while only nichely grabbing hybrid inf and taking full advantage of the new cannons