The issue is prog and world firsts.

It's easy to say that the freedom of complete movement is trivial when you know the fight, but for those first clears, melee uptime is a huge issue.
If Phys Ranged DPS dealt the same damage as melee, then the lack of movement penalty would mean they'd be way more preferred for world first attempts.
The lack of damage is made up for by their utility, not the other way around.