IMO a way to fix Superman *within the context of the DC universe* is to shed the mentality that he must be literally best at everything.
Remember, it was only until very recently that the Flash, a metahuman who is the living embodiment of a "Speed Force", was allowed to be shown to be faster than Superman.
Superman, in his own comic, doesnt hurt being the best at everything. But in the shared universe that the silver age increasingly forced, that the modern age outright assumes, it lessens the entire DC pantheon.
My fix? The mindset should be subtly shifted to being something like "2nd best at everything". Let Flash be faster, a tad. Designate someone to be stronger (gasp!), but barely - maybe Wondy or Barda, someone in the JLA pantheon.
Part 2, I'd increase his powerset. I'd given him dozens if not 101 powers. A bit of this is a harkening back to silver age when it seemed Supes pulled a new power out his arse every issue. For modern sensabilities, I'd ground it into something like marvel's take on Eternals - they're basically energy manipulators that gives them supes-type powers along with force/heat emission (from eyes, hands, and omnidirectional bursts), tp/tk, matter transmutation, shapeshifting. In a sense, I'd end up merging Supes and J'onn into a single concept.
And/or treat his power level like Apollo in the earhly Authority books. He was insanely powerful but his solar battery was portrayed as more limited. He would pull Supes-level stunts then be reduced to human levels until he could recharge.