I'm going to assume that Doran Ring wasn't changed properly
There are only 2 champions who are getting less mana regen now if they built a dring: Liss and Ryze. Except Liss benefits at lvl 2 and Ryze benefits at lvl 3.
I'm guessing in 5.23, they'll remove/nerf the onkill mana regen in order to do what they aimed to do in the patch notes. With perfect Cs, that adds 4 mp5. If they remove that passive, then literally every champion will be worse off at lvl 1 with doran ring than before, but they will be better off at a level determined by their mp5/lvl.
Flat out removing the passive would mandate that most users would be lvl 10ish for the break point. Nerfing it to 2 per kill would require most users to be roughly lvl 5 or 6, which actually seems like a good spot.
If Riot lowered the expected CS rate from LCS level to bronze level, removing the passive would still require the user be around lvl 4 or 5ish in order to break even.