I think you have some valid points and the real crux is coming up with the new mechanic. Trying to justify a new class without a new mechanic seems meaningless. But can that really be done on a forum like this? Do you want people who think it should be its own class to submit new mechanical...
I think this is a fairly interesting topic and got me to thinking about the purpose of feats.
I think by your definition the majority of the features in 5e are not "necessary" either. Out of the 12 classes 4 of them or only really "necessary". And none of the archtypes listed within those...
