While i get your point i think theres a big difference in comparing seinen with a realistic story vs a classical 90s JRPG plot. Thats the thing really, shonen/fantasy/comedy has always sell better than seinen for obvious reasons, is not about the quality of the writing in this case is the fact that most of the anime community what consumes is stuff where they can "detach from reality" thats also why the Isekai genre does so well despiste the mediocre writing, is simple and pure escapism.

Besides, lets be honest, if you make an adaptation of a videogame wich do you think is gonna be the main target audience and the ones that are gonna enjoy the show the most? Exactly, the fans of the game, they're the only ones who are gonna get the references and taking in count that the game has 18 million players is bound to be a success inside its fanbase. This type of shows are mostly fanservice for the players. Imagine if tomorrow League of Legends had an anime, people would flip their shit wouldn't they?

And no, is not sad, is has been proven to this day that the standard high fantasy plot from the late 80s and early 90s is still a very competitive formula that does actually sell, it has its niche. Why it would be sad? Im happy that the such huge fanbase like GranBlue fantasy get a show just for them.