I really don't think he's winging it. Winging it would be hiring and firing a coach every season or 2. Winging it would be running through QBs until finding the one. Winging it would be managing the cap without a plan.
He's done none of those things. If anything, it's precisely the opposite. He's conservative and patient to a fault. He probably gives a little too much rope to coaches. He uses a longer timeline than just about any other GM to manage the cap. He defers football matters to the coaches.
His approach only works if you have a very strong, detail oriented coach like Payton. Allen is really a poor fit, and I think where Loomis falls short is evaluating personnel. He whiffed with the Allen hire, and he was really fortunate with the Payton hire.
I don't like calling him lucky because that sells short the real work he's done over the years. There's certainly luck involved, but you have to have competence as well, especially over a long period of time.
All that said, Loomis is probably nearing the end of his career and I hope they do their homework in passing the baton to someone else. I think some self reflection might be in order and maybe be willing to make some real changes this offseason. Change and rebuilding culture is hard, but worth the effort. Won't always work, but nothing happens if you don't make a push.