after those qualified answers I'd like say soething aswell ^^

Am I forever doomed to recruiting mercenaries if I want hard hitting cavalry, skirmishers, and assault infantry now?
Auxillaries, Auxillaries, but tbh as PedEX and EquEx both are Auxillaries the main thing that changed is that you have to get them outside of italy as those italic allies now are Romans and thus Cohors Reformata.
Also, without Triarii I am not sure what I am going to do about repelling enemy cavalry(?)
that probablywasone of the problems the Romans actually faced in the east and (much) later in the northeast.

(...) other than throwing in a meat grinder of legions.
It's the roman way of doing things. So, as you can retrain your main troops virtually everywhere, do so.

Yet as pointed out before you seemto have overseen/underrated the antesignani which actually fill 3 roles at once: (very heavy) skirmishers, shock troops(tho personally I think Cohors Reformata and evocatido that job fine aswell ) and ("light" yeah right ) Spearmen.

Considering that Thorakitai are considered the latter two and A, are better/even on all accounts than them(ok they have less charge, larger spaceing, less mass and are less trained but wth) they are quite usefull. Plus they are Very hardy which makes them to even betterheavy skirmishers than Thureophoroi (who I consider Cavalry catchers).

If all fails you still have your regional MIC which can pump out myriads of different units.