The answer is very powerful, here are some examples...

Lady Thorn, a Vampire Lord was able to claim what would become Castle Thorn by wiping out the entire Snowbrood clan dwelling within, Lord Harkon a Vampire Lord of the 4th era was able to create a shield that could resist anything short of a Divine Weapon, Rada-Al-Saran in his own words believed the power bestowed upon him by Molag Bal was almost worth the price he paid despite already having the power of the Shehai at his disposal, a power which several thousand years prior he used in battle against the Redguard God Leki.

According to a recent loremaster's archive this power can actually be explained and may also be the reason why Vampires would be destined to Coldharbour when destroyed, one theory suggested that the state of Vampirism connects the Vampire to Molag Bal by a one-way bridge, this bridge is allows the Vampire to draw power directly from Molag Bal but Molag Bal has no influence over the Vampire, this connection is greater the closer the Vampire is too the Daedric Prince, this may or may not be true but could explain the strength of a greater Vampire, they would be drawing power directly from a God, you can read more about it here.

https://www.elderscrollsonline.com/en-us/news/post/62739

Blood Scions though are interesting as their connection with Molag Bal which is why the Vestige is even able to become one in the first place which does contradict this, it could be a case that all Vampires get the power from Molag Bal but with Scions the bridge is then collapsed effectively severering the connection, taking the power and then running with it.