If we were to try to refute that with lore, we might say that a cyrodiilic vampire infestation would be considered a severe threat to Skyrim vampires, who would work to eradicate it as quickly (and likely as successfully) as possible.
But it's not even really a matter of tweaking lore. Cyrodiilic vampires, in the sense of "Vampires that can pretend they're not" are 'been there, done that,' and even besides that, IMO they weren't that great.
They represent a style that has already been put forth. In this new game that is Skyrim, I don't want the same-old that was present in the last game. I want to see what it is that Skyrim has to uniquely offer to me as an experience. And that just so happens to encompass vampires. Not just one clan, but the whole idea of it as it revolves around this far-grungier and darker experience that they're building for us. And frankly, vampires that can't (and don't really want) to hide their nature are things that tie in just fine with that.
Throwing a Cyrodiilic strand, or a Cyrodiilic-strand-lookalike into Skyrim, when what should be there is something new and interesting, seems to me to be wasting opportunity.
The Cyrodiilic vampires would have the advantage of being able to stay in the light, however. And most Skyrim vampires (of which, I think it must be understood, would probably not all be Skyrim origin (because I am sure after all this time and how long vampires live, they travel, a lot. Esp evil ones, lol.)), would have trouble getting around even at night. The Cyrodiilic vampires would act like normal people, living in towns, etc. And, granted that even non-Cyrodiilic (I say this because I can't simply say Skyrim strains, because, again, they may not originally be from Skyirm) can live in towns, it'd be at night when they come out. And I doubt a vampire war would be something so simple. In fact, they may not even kill each-other so soon into the fight. I imagine a lot of battles and multiple fights between the same people before one finally dies. Or they team up and 'cheat.'
I liked the Cyrodiilic vampires. And it is something that has been port forth before, yes, but having them there along with new clans, both Skyrim-originating strains and others who possibly who migrated there, would make it even more interesting! Or at least I think so, lol. Have a good (#) of strains/clans in Skyrim, even including the Cyrodiil-strain vampire immigrants. Hm. And vampire wars! Yes, actually... good example you used. We can have vampire wars. But that's not this topic!!! UGH!!! This topic is about attributes... Sigh... I'll stop this now, lol. Maybe you should start a similar topic to our's, maybe, ThatOneGuy? I am not good at it, lol.