Tacs are harder to kill in Escorts... an escort allows you to play defense through offense... your tac buffs really don't help you do that in the other ships.
That's a great way of putting it.
I usually go after what seems to be the squishy one first. Anything tanky is usually either not a threat or not worth the effort. That, and Tac Cruisers are like 98% bad players and 2% too awesome for me to kill...but at least I have to try. As for Tac Science....they're awesome in STFs.....yeah....but in pvp they're towards the top of my kill first list unlike eng science, which tends to be just really really annoying and not worth my time.
In pugs, my K'tinga usually wears down cruisers and stops healing, my escorts attack other escorts and try to keep them from blowing stuff up. Theres always emergencies and adaptation though. I almost never attack lock box ships.
The Somraw, K'tinga, D'Kyr, D7, Kumari, Xindi carrier, Xindi escort, and the T'Varo are all older than the Constitution Refit and yet they are tier 5. The Constellation is made up primarily of Connie refit parts and it is tier 5, there is no logical reason whatsoever for the no tier 5/6 connie rule.