How strong do you think he would actually be.
We don't know if he is a magic user (his abilities suggest so, but that is unreliable) and we know he was cutting down Shuriman solders by the dozen during "Where Icathia Once Stood" and he was large enough to take the head off of an Ascended. AND that was 3500+ years ago, so he has had multiple millennia of experience and who know what experiences or alterations he's had in this time that has made him stronger.
I believe Jax is probably the strongest "mortal" type champion. And could probably take on some of the "divine/immortal" champions.
I would love to hear how he would compare to a Noxian/Demacian/Ionian/Freljordian militant force