This. Being a vampire in Skyrim has very little cons besides players going "Oh, it makes my face look weird". That's about it. Pure aesthetics. I much prefer Oblivion's vampirism.

TES treats it like an addiction, you grow "stronger" as an effect of the withdrawal and you become more monster-like. Shunned by society and cast out. Because the disease makes you addicted, feeding on blood keeps you from going mental. Hence the nightmares. It's not spinach to your popeye. It's heroin for your anxiety.

Drinking blood doesn't reduce your powers as a vampire lord, which is what really matters.

I still can't fathom how Bethesda reversed and butchered a bit the vampire archetype.

Exactly. And Harkon should definitely know this from experience.

As a lower leveled character feeding can make it so travel and combat during the day is not a headache. Once you're leveled up, on any character, debuffs don't mean much. They mean even less when you know exactly what the debuff is going to be and you have learned the means to counter act them.

Well Harkon is kind of old and maybe he has become so senile that he's just paranoid and doesn't want to come out during the day because from past experience he thinks that the sun will harm him:

Serana: "Dad you can totally like, go out in the sun. It doesn't burn anymore. Your blood boils but it feels kind of nice in this weather"

Harkon: "No! The sun is bad! bad I tell you! Dagnabbit! Soon the Tyranny of the sun will be over! MUAHAHAHAHAHA!!!"

Serana: "Alright Dad, if you say so, It will be over. I'm going to the watchtower to work on my tan if you need me. Love you! kisses!