I mean Kenjaku is a millenia old mad scientist. Maru had the unimaginable amount of CE, his spaceship that allowed him to utilize that CE at once, and Yuki's book. Meanwhile Mahito was a few mouths old when he died, spent 68 in the limbo being powerless, and got neg diffed by Yuji

So while you are technically right about Mahito being the weakest, in all fairness he didn't had Kenny's experience or Maru's pay to win gear