More effective than Williams right now? You could make an argument.
What he is for absolute certain is the most fun to watch score a TD because it's always followed by at least a dozen people going "waka waka waka" (which is often followed by one or more people asking what that means)
I always thought GM's manage the personel. Coaches just coach who they have
Coaches set the depth chart (starters, backups, inactives) and pretty much always have at least some input on roster decisions. It varies team to team on how much.
Generally speaking, if a coach goes to a GM and says "I want this guy cut" most GMs will say 'sure'. Asking to sign a particular guy might be a little more difficult, but during the season generally not that much because it's not like a bunch of unemployed, big money free agents are sitting around waiting for a phone call.
Gettleman has always described the Panthers roster as a 'collaborative effort' but he has final say. Rivera actually had final say on roster decisions for most of 2012 (after Hurney was fired).
Cason was a guy Rivera wanted last offseason because he was familiar with him from his Charger days. The question now becomes did Rivera stop wanting him or did Gettleman say 'this guy of yours sucks and I'm cutting him'.
Speaking as both a longtime football fan and conservative Christian, I feel very comfortable saying it was Te-bow's inability to be an effective passer that knocked him out of the NFL, not anything else.