The answer to "Where have all the medics gone" is really we just dont need them for STF's. Now thats not to say they are not viable or helpful class's to have in the team.
I have run close to 100 STF's now and my partners have more under thier belts, so I can speak with a fair degree of experience.
In our best team for STF's we have 5 caitian captains with full ground skills and ground passives. The feline instincts are a huge advantage on the ground, the plus 75% to jump in infected makes bouncing around the room childs play. all five captains are tactical, no medic or engi required.
the runs are smooth and filled with melting borg. if anything season 4 has made life easier for us without having to deal with nodes, we just pulls groups as well like.
If your serious about running STF's on a regular basis, roll a tactical ground based caitian, you wont be sorry!