Basically, Vampire Lords are WAAAAY OP. This isn't my opinion, this is fact. I feel like once you have every perk in the tree, they should be as powerful as they are in the first place. The perks are just icing on top of an insurmountably large cake.
Ideas:
Instead of the drain health spell being a hand grenade of ultimate destruction/keeping me alive, make it an aimed concentration spell like every other vampire uses. One perk tree could be exclusively to make this more powerful, with the final perk in the tree being that it reverts to the vanilla Hnad-Grenade mode (that makes it require absolutely no player skill whatsoever to use, but hey, you've invested perks so here you go Dragonborn).
Make sunlight drain health, not stamina. Frankly, vampires don't get a wee-bit tired when they enter the sun. They burst into freaking flames and die horribly. You could make one perk with five ranks of 20% sunlight damage reduction, such that if this really annoys the player they can do something about it if they are willing to spend the points.
Make the raise dead spell have differing levels. It's a bit OP that you can just resurrect everything you kill at its full power, especially when killing them is just one Hand-Grenade of life drain away. Maybe at first you just get little ghostly versions of them with a SetLevel(GetLevel()/2), and as you put perk into a tree branch the setLevel divider goes down by .5 until it hits 1, and then by .25 each rank after that. (Making it such that at 1 rank they are at 75% power rather than 50, and at a full four ranks they are at double their initial power.)
You could even have a setAlpha() function that changes its magnitude according to your perk rank such that they are "more ghostly" at rank 0, a little less at rank 1, fully opaque at ranks 2, give them a cool FXShader at rank 3, and give them an even cooler shader at rank 4.
I just found that this spell was either OP as heck if I used it on a strong enemy, and way underpowered on weak enemies. Doing a fractional GetLevel() script would make it more in tune with the vampires level, rather than the enemies. Feel free to do it however you want.
Nerf the UnarmedDamage that the Vampire Lord automatically starts with, and make a tree branch that makes it progressively more powerful. It should scale with playerlevel no matter what, but maybe should scale very little with level to begin with, and scale very highly with level with the appropriate perks.
Of course, if you make this mod, do what you will to balance things. Just please, someone, make Vampire Lords less OP. I wanted to have fun with Dawnguard, and while doing the non-Vampire questline was fun, becoming a Vampire Lord made everything in the game feel trivial. Even Ancient Dragons on Master difficulty were just...easy.