Just checked, a few corrections.
We're both wrong about Demitri vs. Morrigan. In all their fights, they tied, with neither gaining the upper hand.
Secondly, Morrigan's power level is something funny, since she nearly got killed in both fights she had with Donovan, who despite being very powerful, is still human, though he's slowly turning in a Darkstalker. And it's implied that Anita did NOT interfere in those fights. In both cases, Morrigan had to flee to avoid being killed.
Also, Morrigan lost to Jedah during the Darkstalkers 3 events, who in turn lost to Dimitri. That's peculiar, since according to canon, Belial could've eaten up Jedah even in his weakened state.
In short, Morrigan either is considerably weaker than she likes to think, OR her power level fluctuates wildly, meaning she's too incostant to have a definite power level.
Also, it's flat out stated that Lilith is the more powerful of the two by a *VERY* large margin (think the difference between Sakura and Tsunade - that's how powerful Lilith is!), but she consumes most of that power to create a body to interact with the world in.
If you recall, in the canon ending (which is Lilith's for darkstalkers 3), Lilith KOed Morrigan, but used up so much of the leftover power that she was unable to mantain a solid form in this world, and thus was forced to merge with Morrigan again.
Fun tidbit: Namco X Capcom hints that 'Morrigan' is actually Lilith in Morrigan's body, meaning that Lilith is now the dominant mind in the body.