I don't think they should be fired after one year. But there is no question the O-Line was awful last year. And it didn't improve much. There were a couple games here and there that they appeared to get better, but, the bowl game may have been their worst game all year.
The O-Line wasn't aggressive, wasn't mean and nasty, and didn't have good technique. So you can't fix all those things in 1 season. But you should be able to fix one of those things in 1 season.
But, no matter what your opinion. Bronco obviously didn't like it, so he inserted himself into that mess to help fix it. And it got better. Now he has to turn it back over to them again, or get somebody else.