Rhenny
Adventurer
The possible drawback to DM trying to find ways to overcome PC abilities is that the modifications can begin the "treadmill" effect that makes a game feel more artificial (I.e. PC gains +1 to hit, monster gains +1 ac therefore no net gain, so player doesn't feel that PC has improved-the same goes for flight or darkvision or poison resistance,etc.). 5e seems to be designed so that when a PC gains a perk that perk can and will give the PC advantage at least situationally. Therefore, I think it best to design interesting encounters and events and let the pcs special powers overcome or make the situation easier. Flight will help in some situations but not in all situations.As a DM, I don't like any PC having abilities that mean that I regularly have to tailor encounters and adventures to accommodate them. The same goes with disabilities. I never want a PC to play a centaur, as I don't want to be unable to run an adventure that involves a bunch of climbing, or have PCs executed because nobody bothers to take a centaur captive.
There are any number of design decisions a DM can make to rein in the power of a flying PC, I just have enough to think about already, don't want to have to run every encounter through a filter to see if it is still entertaining due to one ability from one PC.
One of the things I did not enjoy about 4th edition was that my high level PCs in the group I was DMing had such predictable encounter powers. Every fight two of them could teleport a bunch of allies around the battlefield. Another could teleport a bunch of enemies every fight. It just made a bunch of otherwise cool encounters boring, it nullified a lot of terrain and positional tactics.
It is not so much that the ability is objectively OP, it is just that I don't want to have to deal with it.
I don't feel that it is necessary for a DM to purposely design obstacles that don't give pc's chances to use their powers.