I think I would increase Nascent Flash's shield to 700-800, but otherwise I would find this change suitable as it hits both the frequency and intensity of Bloodwhetting.

Increasing Nascent Flash's shield both keeps it on level with the other short CDs and allows the Warrior to still save party members, for a time.

For the numbers:

Using these numbers, on the average AoE pull, you can expect 4 * ( 6 * 130) = 3,120 healing potency, or approximately 56% of the Warrior's health. Compared to 4 * ( 6 * 400 ) = 9,600 or approximately 173% of the Warrior's HP, this is much saner number and is possible to misplay and die if a mob pack has particularly strong cast abilities lining up and the Warrior doesn't utilize this properly.

This is a significant nerf in terms of single target and co-tank aid, thus the increase of Nascent Flash to 700-800 shield, which brings it in line with the other short-Cds, however in terms of practical use, Thrill of Battle at 60s should be available for every tank mechanic so the primary loss is in the free duplication and effective 40% uptime of immortality in below-extreme content.

I think this is a much saner baseline. You'll always have it when you need it, but it won't be of so much excess to be comical.

As a side note, I did like damage scaling Nascent better, but I understand the game heavily incentivizes dumping in buff windows which don't always line up with incoming damage.

I think the compromise for adding a few more levers would be looking at ways to incorporate Bloodwhetting as a baseline core mechanic, and then finding ways to, in the mitigation kit, to create high resource investment windows for greater return.

As an example:

Bloodwhetting is gained on every defensive action use with a duration based on the action. (Rampart, Damnation, Thrill of Battle, Holmgang, Nascent Flash).

Equilbirium no longer gains a hot, instead grants a buff that enhances Bloodwhetting healing.

Storm's Path doesn't heal, instead granting Bloodwhetting for a single hit, so around 2s.

This approach doesn't marry the offense and defense together, which to clarify is something I prefer, but instead it'd be giving a little more to think about on the defensive side without explicitly linking the two halves together. YMMV on whether that's appealing or not.