I'm not too mad about the most recent ones added thanks to the EX but looking at all of them now... I'm getting tired of how it seems like every single model needs an extra pipe, a 2nd blade, a flashlight, extendable, rotates, spiky, just.... stop....
IMO, to make a gunblade, you only need a minimum of the following things.
A blade... no kidding.
A gun looking mechanism
Some form of revolving chamber or "cylinder" (and considering Titania's weapon actually looks nice without one, I would even say this is optional)
A trigger
Hand Guard, which... Again, optional but it does help differentiate.
A hammer, ya know that thing the /vpose supposedly yanks back to "fire".
Some of those I can see as optional easily but when I look at some of the designs.... it seems like they make a model then go "too boring, plop an extendo pipe on top of it or a tube here".
Just a couple of examples... The Ruby gunblade has an unnecessary flashlight looking piece on it with a jagged blade... Jagged blade part is "okay" but still, why? The flashlight part, I feel like they could've just easily made the ruby be on both sides of the hilt instead. It just makes it super chunky looking underneath because of this.
Our most recent raid tier gunblade basically looks like a broadsword with it being so wide and square looking.
Hades EX gunblade also just looks... idk, why is it so thick? Fine its crystal, fine its purple, fine the curves to represent Zodiark I guess but it looks so.... blunted (like the sound effects frankly).
Shinryu's gunblade.... I'm not sure where to begin on this one. Jagged teeth curving weirdly with a REALLY weird tip at the end of it... the cylinder is sideways (which arguably is neat but good god the blade ruins this).
A lot of models add some weird ball to the butt of the grip, a pipe on top of the blade, becomes extendable, folding, or just some weird "add-on" as if its not special enough being a part gun part blade hybrid...Imo, they don't need all these gizmos like machinist weapons or for it to look blunt like its a hammer... If I had my choice, I'd say Titania's and one of the early stormblood model gunblades are perfect examples of how to make a decent looking gunblade without overdoing it. Titania's is perfect as it provides the list above and maintains looking unique/separate from other blades, while also providing Titania's flair to it. The stormblood model (I can't think of the name of it) has a large cylinder, straight blade with a sharp curved tip, it's perfect in size and still gives off the hint of being eastern-like.
On that note... So help me god if they don't give us Lionheart for our shadowbringers relic and instead give us some curved nonsense I am going to riot....
TL;DR: There's nothing wrong with simplicity in design.