OK wait...

See for me one-hit wonders are boxers who had 1 big win and then never followed it up with another big win or won a title.

I'm not expecting Turpin to beat someone better then SRR.
But certainly beating a "champion" would merit for me, not falling into this list.
I just don't consider the opponents they beat after good enough not to have them as one hit wonders.

Frankie Randall defended a title several times.
No where near the caliber of JCC but he was a champion and defended it.
That to me does not say one hit wonder.

I'd like to add Nino Valdes.