Being connected to the Sunwell doesn't mean they have to necessarily get the holy energy, since they need arcane magic to feed the mana addiction.
It makes much more sense if they decide to get that energy from there, instead of it just being drawn to them all the time, honestly, and it also aligns with what Danuser explained about it.
https://twitter.com/SteveDanuser/sta...462386176?s=20
You are just assuming they all use the Sunwell's holy energies because it has it and all of them are connected to it, while on the other hand, I have provided rationale as to why they don't follow the light in the same way due to the changes the Blood elves had with their relation to the light over time, while High elves didn't.
And no, obviously the holy energy is there and them all are connected to the same well, however, these two don't follow the light using the same means, High elves have been living in Alliance territory, and there they follow the light in the church.
Blood Knights were the ones who firstly abandoned the light and later on enslaved a light-based being, and secondly started using the reignited Sunwell with the essence of such light-based being, High elves have been following the Church of the Light, drawing the light powers from willpower. Blood Knights are the ones who recovered their faith and also use the holy energies for their powers.
And also, no... Blood elf priests don't have a fancy name, and that doesn't mean they aren't intrinsically related to the Blood Knights...