@BalanceTeam, is my insight to the Kassadin Ulti-Range Change Correct?

So about the Riftwalk changes. Obviously, Kassadin was just insanely mobile and had to be nerfed. However I was wondering why the numbers were specifically changed from 700 to 450?Is it because 450 is exactly enough range such that if he can cast Null Sphere (Q) he can Riftwalk into the fight and W his target? My math was as follows 600 Range Null Sphere = 450 Cast Range Ulti (with 150 AOE damage range) + 150 melee range W = full combo at 600 range.

This allows Kassadin to properly engage on out of position opponents, but does not give him the egregiously large cast range prior, which was 700 (which is nearly double flash). This also allows him to be auto'd by most ADCs while engaging such that they can actually trade with Kassadin, whereas before he could get in and out without much interaction.

In addition, if my math is correct, Kassadin can now cast 5 Riftwalks as well as get in a Q+E rotation and go OOM with at level 18, where before this change, he could only cast 4 Rftwalks, as the 5th was uncastable without mana runes, a second mana item or landing a W while on low mana.

PRE NERF RIFTWALK (75+150+300+600) = 1125 mana Q=90, E=80 1125+170=1395 total cost with 4 Riftwalks Kassadin at level 18 with fully stacked = 2188 2188-1395=793, which is not enough for the 5th Riftwalk without a low mana W or second mana item. Total Travel Distance-2800

POST NERF RIFT WALK (60+120+240+480+960) = 1860 1860+170=2030 Total Mana with is 2188 2030 is less than 2188 Which means now, Kassadin can comfortably cast 5 Riftwalks, Q+E and then go OOM, again ignoring a low mana W or a second mana item. Total Travel Distance-2250

This frees up Kassadin's item build just a bit, as, even though you could go + it delayed your actual power as your stuck building mana items for quite a while and is a bit greedy. I may love the Riftwalker but I can certainly understand why the Riftwalk needed to become a Riftstep. Plus the total distance traveled (assuming movespeed is equal in both cases) is only a loss of 550 in this example, which isnt the worst thing in the world but makes Kassadin much more balanced.

Anyway, feel free to critique my math/thought process. This is my first post like this and I would like some feedback!