We probably should break it down at every level with fixed AP amounts instead of fixed health.
Please note that if targets have lower health, Evelynn does less damage the old way.
Rank 1 R Evelynn with 100 AP
200 dmg new - for 200 dmg old, target must have at least 1250 Health
Rank 1 R Evelynn with 200 AP (should be possible)
240 dmg new - for 240 dmg old, target must have at least 1412 Health
Rank 2 R Evelynn with 100 AP
320 dmg new - for 320 dmg old, target must have at least 1524 Health
Rank 2 R Evelynn with 200 AP
360 dmg new - for 360 dmg old, target must have at least 1636 Health
Rank 2 R Evelynn with 300 AP
400 dmg new - for 400 dmg old, target must have at least 1739 Health
Rank 3 R Evelynn with 200 AP (I doubt a 100 AP Evelynn exists)
480 dmg new - for 480 dmg old, target must have at least 1778 Health
Rank 3 R Evelynn with 300 AP
520 dmg new - for 520 dmg old, target must have at least 1857 Health (roughly where most champions have Lvl 18 base health)
Rank 3 R Evelynn with 400 AP
560 dmg new - for 560 dmg old, target must have at least 1931 Health
The new numbers I think will improve Evelynn's mid game, but won't be of much help towards the late game when every champion in the game has base health that exceeds the listed values. It simply won't be smart to be the first initiator, which means Evelynn will have to wait for another teammate to make the first move and drop those health bars below these listed values.
That kind of sucks for Evelynn mains that have grown accustomed to not relying on their team for initiation.
AD Bruiser Evelynn is left behind in this scenario. Her old Ult was a perfect initiation that didn't rely on her stacking AP. She will have to build Hybrid to even get close to the old numbers, and it won't be effective at all against a Tank or an enemy AD Bruiser.
This is a nerf to First Initiation or high health initiation attacks, and a notable buff for mid/late fight engages. It's a notable change of how Evelynn should be using her Ult.