So, I did the math and I guess that we know the characters’ base-HP “scaling”. The base HP starts at 80 with an increase of 9% per level, including level 1.
For reference, if you watch the gameplay at level 1, the HP of the character (Amara) is at 87. 80 x 1.09 = 87,2 which gets rounded down to 87.
The same goes for the Promethea gameplay which starts at level 10 with HP of 189 and the Gameplay from the reveal from the Lv 25 Operative’s HP of 689, which all fit the formula.
So yeah, the scaling seems to be pretty flat HP-wise, which I like. If we go off of this formula, the base-HP at Level 70 should be at 33.338 HP. I find those numbers easier to grasp than HP in the hundreds of thousands or even millions (for comparison: at Lv 72 base-HP in BL2 were at over 530.000).