Curtis Samuel was a good signing, I think his injury is worse than expected.
The signings of Austin Johnson & Dewaune Smoot have been good. Casey Toohill has been decent as well.
Not every signing is a home run. It happens.
This sums it up, right here.
Reid chose Mahomes, not the other way around. II doubt that Mahomes would be have had the success in the NFL if he weren't teamed up with one of the best offensive coaches in the league.
I cannot foresee the Bills outright cutting Dawson Knox. I know he makes a lot, but they do value him. Although, I can see them asking him to take a pay cut.
The others you mentioned, Jones, Douglas & Milano, I can see being released.