well, against similar mk levels of ships, fleet starships seem to do fine
(except for the zenith one - as i recall it has a weird 0.01xpolycrystal mult, making it useless vs tanks).
Siege starships, back in their old old form of engine destroyers might have been useful, but now we have riot stars for that.. and honestly, thinning out the enemy by engine damage is one of the better ways to deal with anything.