Well-since the whole point is to go to and win Superbowls, I have to say he's been as successful as anybody in his time here. The Patriots and Seahawks are on equal footing, but then, the Patriots must suck because they booted Tebow as well.
And if you think signing Peyton Manning doesn't count, it can only be your bitterness talking. The no brainer wasn't so clear at the time, because nobody was sure he'd still be Peyton Manning after the neck surgery. And there were several suitors, but he signed with Elway to win a championship in Denver. Even agreed to the pay cut the last year and ended up with his 2nd ring, as well as earning his money back. So go ahead and say he sucks at signing free agent QB talent, while discounting the best free agent QB signing ever.
Elway also didn't pay Brock Osweiler $72 million, or give Malik Jackson $95 million, or re-sign Julius Thomas to a huge contract. Sometimes the best free agent moves mean letting somebody else overpay your own free agents.