It looks great.
Final Fantasy has always contained comedic relief, but it has not always been great, colorful high fantasy.
Final Fantasy II literally only has comedy in NPC dialogue, and in one or two interactions in the main story. It was incredibly melancholy, and literally featured monsters summoned from Hell by the Emperor of Palamecia.
Final Fantasy VI is set in a steampunk fantasy world with the majority of its color palette being greys, blacks, browns, and beige/off tan colors. In the second half of the game you are thrust into The World of Ruin with a deep dark blood red sea, maroon sky, and desolate earth as far as the eye can see with the exception of some scant forests. For every moment of comedy, there are two or three of incredible gravity. This includes a scene that you have to actively and somewhat RNG based avoid wherein Celes attempts suicide (unless you get Cid enough healthy fish). Bereavement is a common theme for no less than 1/4th of the game's cast.
Final Fantasy VII is similar to VI, except in a slightly more modernized setting. You play eco-terrorists trying to take down a world spanning Electric Power company that's bleeding the planet's life force dry for profit and control. It is only due to a plethora of mini-games at the Golden Saucer, along with the comedic relief elements that are usually present in an FF that the player is distracted from how incredibly grim the story actually is, being that it culminates in a rather Lovecraftian alien parasite being melded with a human fetus to create a super soldier who then becomes the will of that parasite, and attempts to break open the planet with a giant meteor and feast on its life force to become a god.
There is more whimsy in the next three entries, but none are without deeply existential questions and themes.
FFXI was a brutal, death filled MMO with absolute truck loads of comical relief and whimsy in the cutscenes, because the gameplay itself was slaughtering you every day. Even so, its more serious cutscenes are some of the most serious in the series with incredibly high stakes.
I don't think FFXVI will be absolutely serious all of the time, but even if it is, it will be hard to be more serious than entries they've already given us in the past. The trailers we've been given have been mostly focusing on the eikons/eidolons/summons, as well as the combat, since Final Fantasy has been moving towards action game for the last decade now. I am certain there will be NPC distractions and some comedy here and there within the more personal moments in the story, rather than the grand stakes that is the overarching plot.