In a way, I think his experience as a DB coach may have hurt Walton.
I think he came in and saw a lot of things that he wanted to clean up, just as a matter of what is good and bad practice. That carried into the overall scheme that he wanted to implement, choosing to coach up the players rather than scheme to their strengths.
And of course Fisher wanted him as they actually tried to get Walton before. Not taking the assistant coaching job that the Rams offered him earlier probably hurt his development as a coach regarding the transition from position coach to coordinator.
Finnegan just struggled, and I think in his case it was an attempt to teach an old dog new tricks. It's a shame that he feels the need to lash out at Walton now.