Verticality and flight are two entirely different mechanics.
I can climb up on a roof. I can scale a mountain. I can climb a tree.
I cannot fly.
No CRPG, from the old school TSR Gold Box games, to date has managed true flight.
Even games such as Witcher 3 failed to manage flight - they had some flying monsters you could "ground" by shooting a crossbow at them, but then combat took place against a grounded creature.
Solasta is trying - but even their flight has a great many issues, and will not function properly over certain terrain features - nor can a flying character follow the non-flying characters across terrain.
I suspect due to the complexities and intricacies involved no CRPG will involve real flight and aerial combat in a satisfying manner without some form of advanced VR or Holographics.
CRPG's and D&D computer games have muddled through quite well without flight over the past 30 years - and can muddle through quite well without it for a bit longer.
There are plenty of other game mechanics they can advance with those resources.
Proper balancing of verticality, lighting, mobility, advantage/disadvantage, barrelmancy, movement, itemization, class features, spell/skill usage, map quality, U/I, the list is endless.
Failing to balance those features can kill a game. Failing to add flight and aerial combat are not going to do so.
Let me break a chair over someone's head in a bar fight, and knock them out instead of killing them - I can work with that.
Let me use some of the damn rope I keep finding to tie up the guy after said fight, and question him. I can work with that.
Let me use the rope to climb into a pit, instead of jumping around like a flea in a circus. I can work with that.
These are just as much a part of the premise of D & D, more viable from a mechanical and programming stance, and better use of resources.
