For the best and the worst, they are still the ones carrying the industry.
Most of their titles are solid good, where competitors are struggling to pull out a solidly good work out there.
They should pair the author with a veteran for the scenario.
That's kinda what I mean, though. Shueisha and Jump should be working with and helping their creators in every way possible. "Your story isn't really jumping out at readers. We can pair you up with another author to work things out or just give you some pointers." or even just advising on character design, story arcs, etc. If the series fails, that's because Jump failed. They saw enough potential in Kawaguchi to give him two chances so far, but then shrugged when it didn't immediately take off and do JJK or One Piece numbers, and then axed it a few months later.
If Jump doesn't know what readers want and doesn't know how how to support the talent that keeps coming to them, how the fuck do they expect to find the next One Piece or the next Demon Slayer by blindly gambling on random authors and then leaving them out to dry?