Can you link the source on this?
All I can find is the a Manifesto Cyrodiil Vampyrum and it makes no mention of Clavicus 'reversing' their vampiric stage. It just says "his guidance steels our savage craving with reason and savvy".
Hellmouth answered it. And they can walk in the sun, gameplay even shows this. "Avoid daylight by lifestyle". Why would they put that in a tenet if they unable to walk in daylight?
If the cyrodiilic clan actually had some fleshing out, there would have been vampire-exclusive quests exploring vampire politics and survival, almost like in MW and maybe DF.
However, it was a lost opportunity. So sad.
Amiki, it's called reasonable deductions based on the facts provided. From what it seems, Clavacus Vile's pact weakens the vampiric curse, making the vampire less like a vampire when fed and more like their former self. However, because the curse is weakened, so does all the benefits and consequences.
Normally, vampires are fugly 24/7, and being forced to live away from society, or else face termination. With the Cyrodiilic Clan, it's very likely they do not mind losing some strength in order to hid in plain sight amongst their food, and be able to direct their food against potential competitors.
Well it certainly seems reasonable. But it feels very strange that one line of vampires is opposite to the rest. Almost like a mistake was made.
With Clavicus Vile, there is always a price. Remember the Masque of Clavicus?
"The bearer of the Masque is more likely to get a positive response from the people of Tamriel. The higher his personality, the larger the bonus. The best known story of the Masque tells the tale of Avalea, a noblewoman of some renown. As a young girl, she was grossly disfigured by a spiteful servant. Avalea made a dark deal with Clavicus Vile and received the Masque in return. Though the Masque did not change her looks, suddenly she had the respect and admiration of everyone.
A year and a day after her marriage to a well connected baron, Clavicus Vile reclaimed the Masque. Although pregnant with his child, Avalea was banished from the Baron's household. Twenty one years and one day later, Avalea's daughter claimed her vengeance by slaying the Baron."