Suzaku helped Lelouch out a great deal, as much as I am loathe to admit.
Remember after killing Clovis how Cornelia raped Lelouch at first? Well, if it wasn't for Suzaku there, Lelouch would have defeated Cornelia, and then gone against the stronger opponents. He would have been overwhelmed against stronger opponents. In terms even you might be able to understand, Lelouch's has to gain experience levels before fighting stronger enemies, and Suzaku gave him a bunch.