See, I don't really think it's a quality issue with the manga of today versus manga from yesteryear.
I think Jump has just become way less forgiving. They used to be way more lenient, where you'd have series like Magico that were allowed to run for like a year (IIRC) before ultimately being canned.
It's really about pacing. You NEED quick pacing with instant gratification to survive now. There's no longer a grace period, really.
Now, if THAT'S the criteria by which we judge a series' survivability, I can understand the argument. Although, I don't think the pacing was that much slower with the Big 3, really. I mean, with One Piece, yeah it's probably slower than today's hit manga.