Does flying itself kill immersion? No. This is Final Fantasy... There was always a point at which you started flying, well except beyond Final Fantasy X. Overworld monsters were never a challenge, you literally mashed confirm to burn through them without thinking, and when you got to a certain point in the game? You got a Chocobo to avoid combat. You got an Airship to fly over everything. This was honestly an expected addition long before it was announced, at least for me...

Does flying on anything that isn't a Black Chocobo, Dragon/Wyvern, or something specifically designed for flying (like an Airship) kill immersion? No, not really. Though I do wish they didn't go for this ridiculous "Everything has to fly now!" route... Magitek armor? Really? Seriously hope they don't listen to suggestions and give us a flying turtle/bear/lion/etc....

Honestly my only real issue with flying at this point is 2.0 areas not being updated to involve flying; Yes they're smaller zones, but most of them have a lot of empty map space that could be utilized to offer a Lv60 area in old zones that doesn't negatively impact new players, but keeps the old zones very relevant for Lv60 players. If you want to enjoy how grand something is, you can always land near it and look at it on foot... Something like the Dreaming Dragon I still find pretty impressive, because I farmed a lot of Gelato Flesh around it, meaning I spent a lot of time around it on foot. Does the fact that I can fly up on top of it make it any less grand? No, if anything that adds to it. Something like Black Iron Bridge? That is effectively the same as Highbridge for me, except I can fly to the top of it, fly under it, and if I feel like it, walk across it like a normal human being. I can only do one of those things at Highbridge, to me that makes Coerthas Western Highlands far more immersive than Eastern Thanalan, and that's because of flying...