I would imagine the argument is that it is more beneficial for him to get experience being THE guy against pro players every game, including carrying that into the playoffs. Having him sitting for ~9 games a month probably isn't super ideal. Also, they may feel that he still has things to work on in his game. If you're trying to get him to focus on something specifically it probably is better in the AHL where the focus is more on developing rather than the NHL where the games "count". I'm not sure where I land on the debate, it could be beneficial for him to get NHL experience but I also don't watch a ton of Grand Rapids so I couldn't say if he's truly ready. I'm fine with them not rushing him in the end I think. I think next season will be when he makes more NHL starts with Husso and Lyon hitting free agency.
Cossa also missed some games down in Grand Rapids recently so he may be getting over an injury. Lyon is also joining the team again, so this Husso start is hopefully just a blip because of the injury. Better to yoyo Husso than Cossa.