There is that paradax in STO. Escorts tank almost as well as cruisers, yet cruisers have nowehere the dmg of escorts.
I realize there has been a continuous proliferation of survival tools and heals added, but that's kind of a nebulous statement though, isn't it?
For one thing, it's pretty much expected that an Escort will be mostly built 'selfishly' in that all of their powers are either buffing their offense or their own personal defense. (Consider a JHAS or Patrol Escort with 2x AP Doffs, has a total of 12 boff powers and out of that 9 of them will probably have some survival application).
A cruiser built for support can't be built as selfishly. Imagine if you had RSPx2 and EPTS 3x2 for example - great, you're survivable but you're also now ignorable.
Survivability gets even murkier when you add players supporting other players, it's not really 1 ship classes survivability at that point as it is a team effort to keep Player A alive.