A few times I have had to run around looking for antibiotics but i haven't had a single death due to infection. My worst infection was like 17%. I think you must have had extremely horrible luck to be stuck in an 'endless death cycle' due to infection. But one point I do agree with is the dmage they do when you are on a vehicle. If you want them to do this at night, to force players to fight the horde, I think that's cool. But if you take even a single hit on a vehicle you get some kind of debuff. If you take 2-3 you can sometimes have 3-4 debuffs.
I don't think vultures are difficult at all if you know they are there. They do cause what feel like cheap deaths when you are low on health and one ninjas you though. If it's early game and you don't have the ammo you can juke their attacks. When they swoop in for an attack and get within like 10 blocks of you just run directly straight, and a little off to the side, towards the incoming vulture. They don't turn and will generally go back up in the air for another attack. Or use corners of buildings to break line of sight and they will break off their attack. The worst thing you can do is just run away in a straight line with it at your back because it will just chase you at ground level. They get bored after awhile, juke it 4-5 times and it should deaggro.