Funny you mention this OP because I have a character that I only use gunblades with that I focused primarily on ranged damage with, and I definitely do good damage with it. I actually see myself doing more damage than most people in UQs even though I use mostly ranged photon arts. It's all in the way you build everything, and which photon arts you use.
I believe the point of gunblades has always been to use both ranged and melee attacks, which is why they make melee normal attacks recover more PP. They probably figured less people would use the melee normal attack if both recovered the same amount of PP, since its much more risky to do so.
Because the weapons favor melee however if you focus on ranged attack your melee will also get to a similar number. (For people who don't know, the first page of gunblades will only mention the melee damage stat boost, but you can see if you look on the second page it does actually boost ranged damage too, which does also go up when enhancing the weapon, but by a not so much smaller amount).
This is perfect for many photon arts for gunblades as most of the photon arts for gunblades deal either both melee and ranged damage, or only ranged damage. Can you guess which photon art seems to deal the most damage with this character? Blitzfire Barrage it's description reads "Attack by utilizing the unique construction of the gunblade to unleash a simultaneous assault of slashes and gunshots", so this photon art was made to basically be one that captures the essence of what gunblades are, and makes sense a character with close stats in both would do the most damage with this photon art.
The photon art with the second most damage is Aimed Fire an entirely range damage based photon art, because the first hit of Blitzfire Barrage does an amount of damage that is close to that of Aimed fire. But as the description says Blitzfire Barrage follows up with more attacks, that deal both melee and ranged damage. If my melee damage wasn't so close in number to my ranged damage this attack would definitely deal much less damage, and probably not be my number one damaging photon art.
So to me it seems like the reason gunblades favor melee more is because of these photon arts that use both ranged and melee, so that way if you try to balance the two stats you will end up doing a lot of damage with certain photon arts since they use both damage types.
(On another funny note though, even Risa, the ranged trainer herself says the gun part of gunblades suck in her dialogue for the first gunblade client order you can do for her).