Yes, Light-Fire-Water-Shadow make up everything in the Universe. Everything is balanced on those 4 elements. Innates have nothing to do with this balance right? They're simply reproductions of powerful elements that were created for battle purposes.
Simple. Spekkio can't see battles that haven't occured yet. While at the End of Time it seems all battles have been fought, only those in the existing timeline have been fought. Spekkio is saying that once Magus starts to fight at his true potential, Spekkio can learn quite a bit from Magus' strength. A mirror can not show something that is not infront of it. A history book can not teach something that has not occured. The same is with Spekkio.
Thank you ChronoMagus. That seems convincing. So we know that Magus hasn't reached his full potential . . . interesting.