Arabic defective verbs

No, that section describes actual defective verbs in the sense of missing parts of their conjugation, not in the sense of "having a weak final radical" (where "weak" here specifically means w or y). There's only a couple such verbs in Arabic missing parts of their conjugation. So yes the fact that "defective verb" can mean two different things is confusing and I suggest you go ahead and rename "defective" -> "final-weak" in all of the places I just mentioned. You can probably do this easier than I can.

But maybe it should be nominated at WT:RFM first?

Sure, go ahead.

Ok done.