While Ryze's point-and-click root gets a lot of flak, I don't think that's actually what's wrong with his kit. Getting hit by hard CC shouldn't be a death sentence, even if the CC came from a skillshot, so if you're getting killed just from a root, the problem lies with the champion's mode of damage output. In this particular case, Ryze dealing nearly double damage on his Q for massive burst I think is what's causing his root to be problematic on him in his current iteration, and his ill-fitting, LCS-oriented ult is also responsible for creating a huge rift between standard and pro play.
Personally, what I think needs to happen is that Ryze needs to be pushed specifically towards DPS, and should have emphasis placed on his ability to defend himself, rather than his ability to perma-kite or trail an opponent. Because of this, I don't think he actually needs mobility, but he could definitely use some more interactive defenses. Generally, the issue with Ryze to this day is that there isn't all that much he does that enemies can outplay (which makes his point-and-click W all the more frustrating), so when he inevitably gets reworked in the future, emphasis should be placed on the options his opponents have to mitigate his strength.
Personally, I feel Ryze's core playstyle should be the ability to mark lots of targets before spreading a specific effect to them. In this case, Spell Flux should be his way of marking individual targets, and if they stay close enough his Q or W on one target could spread to the rest. Additionally, alternating between Q and E should be core to his dueling pattern. Because of this, I feel his Q should be his only source of damage, and could perhaps have no cooldown on its own, but would require Ryze to "cleanse" his target with E before being able to damage them again (or even just prep targets with E so that his spells can hit them in the first place). Ideally, this should allow Ryze to be a spammy DPS mage with point-and-click hard CC, but in a manner that would allow his opponents to avoid most of his damage if they play well.