Riftwalk change for Kassadin

We all know that Kassadin is in a bad spot right now, but if played well he can carry a team. Without touching his damage, can you make that if kassadin use his ult for damaging a champion he gets some cdr/mana back? For example: ACTIVE: Kassadin blinks to the target location, dealing magic damage all to nearby enemies on arrival. BASE MAGIC DAMAGE: 80 / 100 / 120 (+ 20% AP) (+ 2% maximum mana) Each subsequent Riftwalk within 15 seconds doubles its cost and increases its damage, stacking up to 4 times. Each subsequent Riftwalk after the first one within 15 seconds that damages a champion gets his mana and cdr refunded for 10%, stacking up to 4 times. If you put the ult on a static cooldown like the one on live (6/4/2) it's pretty big. Here's the math:

(Note that this is not the mana/cdr that you get back, these are the total values) Here's the mana that you get back if you use the ult as a damaging ability First use: 50 mana Second use: 90 mana (Instead of 100) Third use: 166 mana (Instead of 200) Fourth use: 307 mana (Instead of 400) Fifth use: 571 mana (Instead of 800)

And now the cooldown that you have if you use the ult as a damaging ability Lvl 6 (Static cooldown of 6) First use: 6 seconds Second use: 5,4 seconds Third use: 5 seconds Fourth use: 4,6 seconds Fifth use: 4,2 seconds

Lvl 11 (Static cooldown of 4) First use: 4 seconds Second use: 3,6 seconds Third use: 3,3 seconds Fourth use: 3,07 seconds Fifth use: 2,8

Lvl 16 (Static cooldown of 2) First use: 2 seconds Second use: 1,8 seconds Third use: 1,6 seconds Fourth use: 1,3 seconds Fifth use: 1,4 seconds

For the mana it's a pretty big buff, for the cooldown reduction it's a nerf only if you use 40% cdr on Kassadin. I mean, you can get the full 40% cdr for 15 seconds even if you have 0% cdr. This would allow for Kassadin players to use Mr per lvl/Ap scaling in their runes, so they can keep the cdr on the ult.

Hope you like that :) Peace!