Yeah I can definitely see this as a problem. But then again, when I look at how many fireballs to kill Strahd I can see why 5e did this. If we use 2e numbers, you could use a wizard/fighter and kill him in a round. Maybe this makes combat a tad too quick and there wasn't much to it? I never played 2e so I'm not sure if this is the feeling you get from it though.
On theory, yes, he can """die""" in one round to a delayed blast fireball. However, he has magical resistance AND good saves that needs to be dealt, is immune to weapons weaker than +2, has a lot of skeletons and a contigency of spells. Contigency of spells allow him to insta cast 3 spells when a condition is met. Eg - When with less than 10% hp, he could summon a horde of skeletons, cast a cloudkill and teleport to his coffin.
On 2e, vampires are also not insta destroyed when they have less than 0 hp.
Did you played BG2? they become in mistform and run towards their coffin to heal. You can fight then on chapter 2 and 6. And they also has a lot of nasty abilities, like inflicting negative levels...
A situation
"I dealt massive damage to him, now he is on mistform, and summoned a bunch of buffed skeletons harder to turn before teleporting using a contigency and fight his skeleton army inside a cloudkill would be very hard. We need to deal with his skeletons and find his coffin before he can regenerate and re attune his spells is far more interesting than controlling and attacking every single round for long hours. The first remembers me about a vampire novel. The second of a mmo..
