To be fair, Cassel barely played in the preseason, and by all accounts outplayed EJ during practice and training camp. In the two games he did suit up and see very limited action in he was 13 of 15 for 83 yards, no TDs/no Ints. Certainly a respectable showing, especially considering he played against the 1st string D both games.
Not saying Meh is anything more than Meh, but he did earn the right to make the roster. Being a veteran of 13 years, it makes sense to have him holding the clipboard and mentoring. Let EJ learn at #3, without pressure, and see how things play out.