D&D (2024) Multiclassing as feats:

[Corinnguard]

I.E: battlemaster could have been a universal subclass for anyone, sure, the martials would utilize it the best, but even a wizard could had have a whack at it as a contingency to spell slots over cantrips.

You don't really need to have the Battlemaster as a universal subclass in order to give everybody access to that subclass's combat maneuvers. All you really need to do is to have that access as a class feature for all of the martial classes. Level Up already does this for its' martial classes. As for a spellcaster like the Wizard, the only subclass that ought to have some access to combat maneuvers would be the Bladesinger. And again that access would be a subclass feature for the Bladesinger. There are btw, a couple of combat traditions in Level Up that do try to combine magic use with a combat maneuver. Arcane Knight and Cutting Omen.