Celebrim
Legend
The first is fine, but in 1E only thief functions were restricted by heavier armor for multiclass characters. On that one you're thinking of 2E.
He's having multiclassing work more like human dual classing. If you were a human dual classed cleric/M-U, your casting ability as an M-U was still restricted by armor. An elf multiclassed in to say Fighter/M-U worked differently, but this was by design and was restricted by harsh level caps.