I don't think this is fair at all, 3 months with Palermo was the only bad one. Benevento who he relegated were in Serie A for the first time in their history. Getting 8th twice with Sassuolo was great and they played really good football. Massive injury problems with a European campaign and selling key players this season but everyone was scared of Brighton last season.
I would never swap Howe for De Zerbi but he will have a really good career as a manager and his next job will be a big club.