Well he was at a stage where he could only be altered through numbers on his kit. If his Q did too much damage, he was oppressive, if it did too little, he was useless. If he was ahead, he would win a fight. If he was behind, he would lose. There really wasn't a way for Ryze to come back if he was behind or be taken down if he was ahead because his kit is always "on".
They effectively changed this by giving Ryze power windows in his passive. Scenario: Ryze is behind in lane, and his opponent knows it. His opponent tries to push the issue and goes to fight Ryze when he thinks he has the advantage. Ryze can kite his opponent with his Qs (given its increased range) while building up his passive. He then turns on his opponent unleashing a slew of spells while his shield keeps him alive to win the 1v1. On the other hand, if Ryze is ahead, his opponent can dodge his Qs and back off when Ryze's passive is about to hit 5 stacks to avoid Ryze's power windows.
They wanted to keep his identity as the tanky battle mage, but they wanted to give Ryze more power when he was behind and more counterplay when he was ahead.