The reason why a Dragalia Lost character is brought up so much for Smash is partially because it's an IP Nintendo owns and is heavily involved in.
I don't see why Granblue needs to be brought up against it when they're two completely different situations not even counting the fact that Nintendo has almost had no involvement with the franchise up until Versus which is a spin-off developed by ArcSystemWorks.
Granblue is CyGames' most popular franchise, yes, but just because something is popular doesn't mean it should get priority on that alone, it needs to be something that benefits both parties and considering it also has licensing issues that prevent the main game from releasing overseas it just doesn't really make sense to me.
At least with Dragalia it's something they own, could use Smash to give it more exposure overall, and also is available in most parts of the world except Europe, to me it honestly seems like the no-brainer choice to me, people are going to bring up "Popularity" but once again, that isn't everything.
Granblue's licensing isn't messy at all. The only reason why they don't bother with the "official" overseas release is because licensing all the collabs they've had is pretty expensive; and probably wouldn't work with the overseas release anyways. They already have a dedicated group of players outside of Japan as well, so there isn't any point. Officially releasing outside of JP is kind of pointless right now.
I don't really see why they would prioritize Dragalia over GBF. The game isn't successful at all in Japan, and is struggling outside of it. While the FE, Monster Hunter, and Megaman collabs all help it out get some fans, the game still struggles to retain those fans. Smash would pretty much be the same, what's the point to do it if people are still not interested?
Meanwhile GBF is getting actual console release (not on Nintendo, but still) which shows where Cygames priority lies. Besides Nintendo owns 10% of Cygames, so they both have a common interest in increasing the popularity of the series.
Besides this isn't the first time popularity played a big factor in who gets added into Smash first. Persona was chosen over SMT, despite the latter being way closer to Nintendo in recent years. Cloud was chosen over a more Nintendo associated rep. Ryu got in first despite SF 5 being Playstation exclusive.
Sure Dragalia is more associated with Nintendo, but at this point Nintendo association isn't the end all be all of who gets added. Especially when we talk about something that hasn't happened yet, such as a mobile character. Really the only exception to the Nintendo tries to prioritize the most popular/well known/mascot character of a 3rd party company is Banjo. But even then Banjo had tons of fan demand, and even Microsoft itself supporting it.