I've been talking about this in discord for a while, mainly amongst staff and in passing with other people, but this idea of Map structures is important to address as a whole. For my point, I want to look at a few maps, mainly Goron, Downturn, (Old)Vector, and then Underpass. It's going to be a bit long and difficult to explain, so bare with me.
Lets start with Goron. One of the biggest issues of Goron comes at the bottom of the map. We added in fall damage prevention on infected spawn to help with maps like this, but we still see issues when more players are on. What ends up happening is the room in the back is barred from others because there is a wall or tankers who are all full irons. On their own, commanders are not that bad to take down. They can take at most a 1v5, and then will be severely crippled for the rest of the game. They can't do much alone, but in groups they become annoying. One infected can only get like 1-2 hits at most on one single person in a group of commanders rushing at them. The solution is to infect other people, but everyones behind the commanders. The only kit to breach the wall and start spreading is enderman, which is horrendously weak. Adding in another pathway could help, too. Another fix to that though, is Vampire fly. They can simply fly past the wall, and maybe get hit once otw in. From there is just another means to pushing out consistent damage, but at least faster than enderman and with potential to perform better (combos are more rewarding because you heal).
The issue I mentioned there is just a horizontal barrier, but the entire concept of vertical maps is a bad one to have. This is where Downturn and (Old)Vector come in. Both of these maps suffer from incredible linearity and difficulty for infected to traverse. You can obviously clear horizontal areas much faster than vertical, and getting hit off the vertical areas means you take fall damage. It slows the game to a crawl and is nearly impossible for infected to do relatively well on. Fly on vampire would help remedy this issue as it would provide another class, like enderman, that can breach the defenses and actually spread the infection. Vector is mentioned on here because the Old one would be a one shot if you got hit off in most cases, and the time it took to travel was insane. The revamp has more pathways and has made the ways to get up much most secure and safe, as well as lowering the overall height of the map.
Now lets look at one of the more even maps in MCI, Underpass. The entrance straight from spawn that leads to the open area is usually guarded like Goron, but there are 2 other sides you can collapse from, as well as plenty of other spots people go to. You can slowly make your way from outwards in, and then kill the game that way. Vampire fly accelerates the process by letting you get to the side spots quicker, and helps liven up the game and increase the pace.
Vampire fly, though not necessary to help all maps, adds another dynamic to the game and helps better a class that is severely lacking in relevancy. My standpoint is that it fixes core issues with maps without having us edit them, as well as accelerates the pace of the game a bit more while keeping things engaging and fair. The kit itself shouldn't receive changes (like its healing or armor), but this allows it to infiltrate and deal with humans better. We also don't have leveling on paths, so the strength of it won't be any higher than what it is right now. Thats an issue we had with Vampire on PM, where the healing it got ended up being ridiculous with fangs. I can't remember the exact numbers, but it made the kit FAR stronger than it is now. And, worse comes to worse, the kit can be nerfed or reverted if it throws the balance of the game off that much. As of right now though, maps are a huge issue and a very easy solution is to add fly to Vampire to make it useable as well as another tool for infected (as we don't have really enough for them right now, imo)
To clarify, this doesn't reflect what the staff team as a whole believes. I want to bring this part up as its important because it tackles two different aspects of the game, and bringing this point forward adds to the discussion and enhances the details we have to look at when voting one way or another.