For an antagonist, Shuyin sure is popular among FFX-2 fans. Unlike Lenne and Yuna, who were too "saintly" for a player to relate to, Shuyin was always honest to his feelings and practical to the core. That being said, I don't think I'll ever like him that much, though I do enjoy his interactions with Lenne.
If Lenne ever had any rebellious side, it was probably overshadowed by Shuyin before anyone had a chance to notice. Without Shuyin's black-or-white sort of thinking, Lenne wouldn't have appeared as caring and gentle a character. They might be opposites at first glance, but they're also similar in many ways.
Both Shuyin and Lenne were the idol of their time - people of Spira must have found as much excitement in Shuyin's Blitzball as Lenne's music comforted them. While not expressed explicitly, their love was likely a publicly celebrated affair. Otherwise, a commoner like Maechen wouldn't have known so much about the history behind their tragic end without seeing it with his own eyes.
Having a similar social status is crucial to any relationship that seeks long-term stability. Two people don't necessarily have to start from the same ground, but it's important that they walk towards a similar destination of mind, for which both materialistic and spiritual needs play equally significant roles. With more than enough fame rolling in their lives, all Shuyin and Lenne ever wanted was some peace and quiet, yet the era they lived in forbade their one wish from happening. "Life is never perfect" - while Lenne accepted said fact with grace and resolve, Shuyin refused to look at reality and took extreme actions to prevent his own dream from shattering. We can't say Lenne's decision was better than Shuyin's, nor can we say Lenne was a more pessmistic person. In fact, it must have taken more than courage on Lenne's part when she cheerfully stepped onto the stage of no return.
It's true that Shuyin didn't want Lenne to sacrifice herself, thus leading to his crazy idea that destroying the world would solve all problems. However, he would stop running into extremes whenever Lenne told him to. One can say it's the power of love, but I believe it's more basic than that: Shuyin respected the will of a person he most admires, otherwise he'd have let his possessive nature take over long ago. His love for Lenne had always been of the purest form and Lenne recognized that, as shown during their final goodbye to Spira.