Internal problems
If traversing the Path of Control was necessary for a Vampire to be able to do magic, it meant that, although vampiric body and power are not 100% compatible with mana, the Path of Control could be used so that vampiric power, body, and mana could coexist.
According to Matt's research, the vampire's body is compatible with mana, not 100%, but a percentage above 50%, and that is more than enough. The issue was that vampiric power is not only an element but also an attribute. Being an attribute, it has a personality that is a bit tyrannical, so it does not tend to allow mana to coexist with it, even though they are compatible to some extent.