I think many of those "experts" you defer to, are just the yahoo's on here that haven't a clue. They do spout lots of authoritative opinions that are strongly backed by zero evidence and little if any basketball knowledge. So be cautious.
I have not read any opinions from
real experts that mirror those sentiments. Doesn't mean these statements are wrong. I just haven't seen anyone whose opinion I consider 'accurate' say these things. Let me know if you have stubbled across any real (commercial press types) that have identified those specific weaknesses.
IMHO (not an "expert") Gillis has a knack for being in the right place at the right time defensively and offensively, and is a considerable athlete with good quickness and good anticipation. Morton does seem a bit foot slow, but we may be looking at his efforts verses world class speed. He may be just fast enough to provide sufficient defensive pressure on the opponents #1 to do the job. Also, just because he plays the PG doesn't mean he guards the opponent's PG.