I have at least three other options to suggest...that are all unlikely to reopen the "win gap" between diamond players and bronze.
Option 1: Buff Ryze's speed. Ryze is so movement constained that most players take movement quints, stormraiders, ghost AND flash. That's ridiculous, and still sometimes insufficient. Would benefit bad players as well as good, so would probably not reopen gap.
Option 2: Buff his base health. Would help bad players survive longer, so would probably not reopen gap.
Option 3: Give him some escape...here's my suggestion. Make his ult launch region slow enemies that pass through it. Then bad players, who have not mastered the ult, could at least use it as cover to allow themselves to flee bad situations. I suspect good players would mostly still use it as currently designed. Probably would not reopen the gap.
If the gap does reopen...possibly consider increasing the cast radius/hit box of his two point-and-click spells, w, and e. Q's is already quite large. This would help bad players (sloppy mouse play) hit more often, but since good players already hit, probably wouldn't alter much for them.
I didn't play ryze before the rework, so don't pine for the good old days, but stats don't altogether lie...Ryze has been laughably at the bottom of win percentage, across the board, for some time now. Why the lack of love?