I dispute that. He knew the situation he was getting into. Allen wasn't some first time coach coming off winning seasons. The probability of him being here must longer was not a safe assumption.
I mean, he didn't know that Taysom Hill, his top two WRs, and starting QB would miss half or more of the games. He also didn't know that the middle of his offensive line would be hurt for most of the year or that Kamara would miss a significant number of games.
He's a big boy and knew the risks, but he was still handicapped in ways that he did not expect when he took the job.
Still, I think he's a solid OC, miles better than Carmichael, but I also don't think he's an amazing OC that we can't upgrade.