This is exactly the point, we didn't know he could handle that job, because he was a rookie and we needed to get film on him actually doing it and he needed snaps to get better at it. As had been stated, Chef would have been counted on this season for coverage teams (at the least), and you don't want scrubs out there because special teams are actually sorta important. It makes no sense at all to have a guy like Chase Allen out there to start on special teams when he's not very likely to make the actual team, that's what the fourth quarter of preseason games is for.
I understand that everyone is all in their feelings because we lost Chef, and he was expected to play a big role for us this year, but we've not actually seen him play a single snap of defense in a game this year, so the reality is that we don't know what he would of brought to the team. What would people have been saying if the same thing happened to Dion Jordan??? "Oh no, we lost a top three pick, he was going to be awesome for our defense this year". I'm certainly not saying that Chef is going to be anywhere close to the dumpster fire that Jordan was, just saying that a little perspective is in order. There is no way to know how a rookie is going to play in the NFL until he actually does it.
I understand everyone is a bit punch drunk from all of the injuries we've had at key positions, myself included (I actually reverted back to my old user name!), but saying the Chef injury is on Gase is misguided and unrealistic.