Thematic wise you have a lot of FF in XVI. Hell, the theme song has them listing the most recognizable summons in the franchise. From the character designs, the Ivalice/Eorza like setting... In terms of overall aesthetics, it definitely looks and feels like FF.
Gameplay wise it's very different but I think that's always been a thing even before FFX. Going from FFVII, to FFVIII, to FFIX, gave us the widest swing in terms of battle and customization mechanics in the PSone era. The way you play FF has always varied, with the only common factor being ATB turn based battle and some magic/RPG trappings.
Now that the technology has evolved and expanded we're seeing just how far they can push the structuralism that makes up each game's style of play. It's creative evolution.
While this is true, and XVI certainly appears to have the typical FF tropes in place. There are certain qualities a series has that many fans won't want to see the back of.
For example, I'm all for the shift towards action RPG combat and think its long overdue. While I can enjoy both turnbased and action, I would always choose action. But, I totally understand why other fans feel its stepped the series away from what it was.
If they do remove party members it will change the feel of the game significantly from what FF games are.
I'll still play it, but I don't think XVI is going to fit what I normally play an FF or JRPG for. I think its shaping up to look like a fit for what I'd normally play a Witcher or perhaps a Naughty Dog game for.
And I think that might be the problem. I love The Witcher and several Naughty Dog games, but I love several JRPG's too. I play them for different reasons, and FF moving into another space will dillute the games I enjoy in the JRPG space.
For me, I'm going to be down to pretty much just Tales Of and Ys for action RPG's and Dragon Quest and maybe the occasional Atelier game for turn based - heck, the latter of which I don't even play for story or combat, I play for the same reasons I play Stardew Valley, Minecraft, or maybe Animal Crossing... a casual crafting/grind game I can pick up and put down on the Switch.
So, it feels like I'll be gaining something in my western rpg and action collection but losing something in my JRPG collection.