Stacking extra attack

[Psyren]

So a Fighter that multi-classes into a Wizard loses 2 levels of armor prof? And what about shield prof? Shields will usually be the more problematic part for casters not armor.

They don't "lose" anything, they just can't cast Wizard spells while wearing Medium or Heavy - similar to Slipjig's proposal.

That wouldn't change the difficulty of writing the rule though, ending up with exactly what Slipjig wrote.

It's functionally not that different but I think it would be more intuitive in practice.

(Note that this is purely a suggestion on my end; I'm not the one who has a problem with wizards in plate.)