Now you're just making assumptions. I don't know how many times I needs reiterate this. Piercing Talon is always a loss. It's a meager 150 potency. Therefore, it takes four uses for it to surpass Full Thrust in damage. Except... it gets even worse because by breaking your combo, you'll lose out on the subsequent 370 from Fang/Wheeling, which go onto buff the next hit. Even Raiden Thrust, your weakest ability, necessitates three usages of Piercing to eclipse its damage. This has long been mathed out by theorycrafters, and one of the principle examples for range attacks not breaking combos. Piercing Talon is so laughably break, Dragoons defaulted to their AoE combo in E8S. And even that's still a loss unless you're on Fang/Wheeling/Raiden as they're only 10s long combos for some odd reason.
All of this also calculates in the maximum amount of greed.
Ironically, you dismiss your own argument by saying "those two GCDs don't matter." Then why even have range abilities to begin with? The whole point behind their existence is having a supposedly reliable ability to press when forced to disengage for a lengthy enough period you can't keep your GCD rolling. Monk literally doesn't even have one, Dragoon's is so embarrassingly weak they may as well not have one and even Samurai can lose out because it's always a gain to keep your combo over Enpi spam unless you'll lose several GCDs. Ninja is the only Melee with some degree of wiggle room here. In fact, Ninja has typically performed second or even first among Melee in several fights throughout this expansion. Could it possibly be due to the rework allowing it to weave Mudras at range, thus giving it upwards of two GCDs at full potency before dropping to Throwing Daggers? I doubt that has anything at all to do with it...
This has nothing to do with balance in a general sense but the fact Melee range attacks have virtually no purpose. That, and your opening argument doesn't make sense. Per my prior example, Piercing Talon not breaking your combo wouldn't change anything else except to give Dragoon an actual GCD when forced off the boss for long periods like E8S. You'll still want to greed your combo and avoid using range attacks because they're weaker. Having to default to your AoE combo or do nothing at all is simply bad design.
No, they often don't. This is why Dragoon dropped to being the weakest non-Range DPS last tier, and Monk barely above it. Neither had any way to combat the frequent downtime in Verse whereas say, Ninja did. Keep in mind, this is the same balance team that went on record saying, "We don't balance Bard and Machinist around Piercing" and then were baffled why Dragoon was basically mandated in every party and why Bard always had such absurd balance creep. In took them four years to realize that was a problem.
And I, equally, don't understand how making Melee Range attacks non-combo breaking takes away from that fun. Like I said above, you'll still prioritize keeping your combo GCD rolling above all else because delaying Full Thrust one GCD to hit Piercing Talon will be a loss. The only difference is you'll actually get to use Piercing Talon or consider spots to put it instead of simply sitting in the corner and sucking your thumb.