Tournament practice shows that the alternate unit is currently much stronger. For example, in RTA, the higher vampires were buffed even further to balance things out. If the upgraded unit cannot deal more damage than the alternate unit, then what is the point of it? It has less health, less speed, and a mediocre retaliation against paralysis, which can decide the outcome of a battle. When dealing damage, I would rather deal damage with single spirits and have the ability to paralyze than simply attack without retaliation and do nothing else. Moreover, the lack of retaliation here is relative, because when the enemy gets a turn, they can deal significant damage to the vampires with their own retaliations, unlike when they are paralyzed.
Even with the reduced chance, paralysis still has about a 30% chance of occurring. And when it does occur in an attack, it provides two retaliations at once:
1) The enemy does not retaliate against the attack because they are paralyzed.
2) The enemy does not retaliate against the next attack that wakes them up.
And this is in addition to the fact that the paralyzed enemy simply skips their active turns. And this is in addition to the fact that the alternate vampire units deal maximum damage (13) with the attack that wakes them up.
I won't even mention that several squads of alternate vampires can easily defeat any number of enemy units without losses if there is skillful use of the "Confusion" spell. This squad will simply never get to move and will slowly dwindle.