Glare is a good strong ability and yeah it can stun everyone around(or actually just knockdown, its kinda hard to stun everyone), however counterplay to glare is extremely easy. Just dont stay near the vampire with all your squad. You need just one person to cuff them, others can stay nearby and keep their stun with disabler or come close, stun and walk away. If security do this, vamp has almost no chance in escaping being cuffed and detained. Yes, it requires you to have multiple security on sight but its not bad imo, lone sec shouldnt easily arrest a vampire.
Dantalion on lowpop or with low sec team is an issue yes. While his general powers are strong enough for escaping and fighting, having multiple thralls ontop of that makes this vampire the strongest of all four. If you are facing a dantaion as lowpop sec, just unload your lethal weapons. Space law allows you to use lethal equipment against a group of enemies, especically if you are outnumbered. One by one you will kill their thralls and leave the vampire alone. Just keep in mind that Dantalion can pacify you, making you unable to use any lethal equipment or harm attacks at all for about 30 second(i dont know exact time but its long), so you should stay in pair and support your mate with disabler/baton if you were pacified.
In the end, i would say vampires are balanced enough compared to other antagonists. I dont want to mention mindflayer here, the god of unbalanced abilities, even without him we have a lot of traitor items/antags that break the game loop completely making chasing/fighting them almost impossible. If vampires need a nerf, i would say lets block dantalion subclass on lowpop rounds and thats it.