Actually, I think it is possible to do all those things as a PA; the only catch is that you can't do all those things completely autonomously, that is, without the supervision of a doctor (as was mentioned before, it can be online or offline supervision). In fact, I'd say being a PA is far more flexible, since you can actually change your specialty if you like. As a doctor, you can't really change your area of specialty easily.
EDIT: I should say that the scope of practice for a PA in each case is naturally more limited than that of a doctor of that same specialty. In many cases, depending on the state, a doctor can delegate most of their usual activities to a PA, pending final review, and/or with other appropriate supervision.