Vesperia has like...the most broken battle system lol. I thought Symphonia's was the best >.> the lack of broken Ad-Skill, the lack of Free Run, the lack of an overlimit bar made the game a little bit more challenging. S and T-Type added more depth, and Ex-Skills were cool but didn't make the game too easy...
Yuri was really the only true broken one, since he came with the most ridiculous combo artes/skills, AND he had his own personal OL that was ridiculously easy to get. Everyone else is... pretty well balanced, at least on Unknown. You still can't combo late bosses even on Hard because they just hit you out of the middle of an arte or get away somehow.
Symphonia's feels so meh to me. I don't really mind a challenging game, but the difficulty I felt stemmed from the wrong places. S and T-type didn't really feel like added depth to me. It made me feel like I was being cheated out of half the artes in the game. Ex-Skills were almost a complete waste without a guide, and the lack of Free Run felt like a million steps backwards after coming from Abyss. That, and Multibosses were absolute hell for me because I would frequently get trapped while my AI brigade sorta watched me die.
I do think that the battle systems are becoming more balanced with each game, however. Abyss was the first with its type of skill system (I think...) AND the first with Free Run, so naturally they were pretty broken. What I liked about Vesperia was that it was much more balanced. You had to pick and choose which skills to use, so without massive level grinding or the Grade shop item that has each skill cost 1 point to use, you couldn't activate the full brokenness of each character. Free Run was also fixed by giving most bosses giant AoE attacks or by making them all run faster than you (unless you're Repede, usually), so you still had options to get out of sticky situations but you couldn't just run.