this is actually one of the most limiting things i can think of to do.
i've always felt its more important to fly what your comfy with first then figure what ship to stick the captain in.
ive seen great success with engineering escorts, or science escorts, or tactcal cruisers (excelsior only) or science cruisers or even tactical science ships.
mixing and matching is half the fun. (im not saying they all need not fly their "class" of ships but that only limiting to those ships may hinder your efforts at pvp.)
Sorry, but I have to completely disagree. Really good teams can get away with running hybrid fail boats simply through strength of teamwork. But an engineer escort is never going to be as valuable as a tacscort or sciscort. An engineering or tactical science vessel will never be as valuable as a sci/sci.
When SP was first formed we had almost the exact same mindset as these guys. Have a preset team (back in the day was 3 sci/sci, one eng/cruiser, and a tac or sciscort), have multiple people able to fill multiple roles so that we can run that setup as much as possible, and practice like mad. Our motivation was that we had something to prove -- and that original team became more or less unstoppable.
I think it's somewhat unfortunate that we've fallen away from that ideal a bit recently, but if we had started out running whatever the heck we wanted to we would have never gotten to the point we're at now.
Creating a great PvP team isn't rocket science. Assuming they aren't hopeless players, If these guys follow through with the plan they have set out it'll only be a matter of time before they can best every fleet that has less discipline -- including the present TSI and Pandas. Don't discount power of a fleet that has something to prove and a solid plan to do it.