Is he? Seraphina is outstanding so i am not sure...
Since he copy others, yes he is ^^
but according to uru-chan's chart she made about the school ranking sera is the most powerful and arlo is third with someone missing in between. It seems like adding all the charts and hints together that john is higher, but it could be that as uru-chan said that there are different ways to determine rank. Sera could be born natural talent were as john could have worked for his. Then again is could be that he is strong because in the beginning john kept deigning that he had am ability, but the only one who would know for sure is uru-chan (≧∀≦) so we will just have to wait and see ٩(๑❛ᴗ❛๑)۶ ╮(￣▽￣)╭
I wonder how seraphina is going to be like after finding out john is stronger than her! (=・ω・=)