LBE – minimal balance changes for Heroes V 3.1.

What do 2-4 heroes have to do with this? 5 are being considered.
Based on vampires alone, strategies can be set for both capturing the Dragon Utopia and early breakthroughs of high levels. Is 50% really not enough?

There is also an option to shift their damage\attack into another parameter so that the drain doesn't play out as strongly.

It's bad to ruin a unit just for the sake of a breakthrough. Then you might as well start cutting shooters, casters, and ghosts.
To stop vampires in the corner + Dragon Utopia BDP from being viable, it is enough to remove the clunky 20% HP penalty on raising. Although you already removed the BDP for the Necromancer anyway, so what's the problem?
In the endgame, vampires (if looking at the upgrade) are mediocre fighters regardless.

There is also an option to shift their damage\attack into another parameter so that the drain doesn't play out as strongly.

Make even more tanks, besides zombies and ghosts?