The gap matters, for many reasons.
One most obvious is that there is 4 DPS spot. You bring 2 Casters or 2 Melee, but if you bring 2 Ranged you are punished with low damage despite the double range mobility bringing nothing to the table. Addle has more presence than Tactician&Co. In PartyFinder you can easily experience parties limited to a singled ranged, that's mainly why I learned Samurai. And it's not only based on my experience alone.
You can't force the ranged role in parties either, that's a terrible and lazy idea. It's like being forced to bring your little brother or forcing someone to play the thief in cops&thief game. No one would want to be forced to play something especially if they damage would not matters.
Movement tax why not. But makes it worth something.
SMN is a monster right now, even post nerf. It has a valuable raise that brings a lot during progress, much more than mobility.
Again, despite the mobility advantage, ranged were lower than any other DPS on the first weeks, exactly where mobility should have shine.
And again, ranged don't have rDPS nor utility that would excuse such a gutting.
The ranged role is not fine. It went from a valuable support that could make the difference with manasong and mitigation to just a DPS with one mitigation and some extra for some.
The big support part was removed/gutted from rangeds and it wasn't replaced with anything.
Ranged role needs a rework, you can't slap a silence on it and a 1% stats to everyone and call it a day.
Casters have more support than ranged, they have a high mobility and remains top rDPS.
There is no mechanics that requires you to run like a monkey everywhere and during big mechanics, especially in ultimate content, you can't even target the boss. The GCDs loss is not that important, the uptime lost to mechanics doesn't makes the difference unless you compare Casters and Melee.