Zenos seems to be a special case even among garleans, but yes, Garleans seem to be physically superior with the weakness of not being able to use aether.

The garlean scientist guy in SB alludes to this. At the time I thought it may have just been propaganda, but then Hien also makes a comment about it not being fair that 'Zenos' i 4.5 has both a garlean body and magic.

Zenos has an artificial echo that lets him use magic, though I think he was also just a super prodigy even before then.