At least, not in PVP anyway. Did some PVP'ing with my fleet last night (should be noted that the ones I was playing with in particular have been doing PVP for years now so they do know what they're doing) in my Ha'feh (just the regular one, not the fleet version) and I was able to survive onslaught after onslaught of two sci's in an armitage and a vesta and Klingon tac in a Bug.
Granted for a long time in the engagements they were not focusing specifically on me (my side had a Wells, an oddy and one of the smaller Klingon vessels. Can't for the life of me remember what it was) but even once they started focusing all of their abilities on me they couldn't take me down for the longest time until a hole appeared in my heals. And that was just the situations where I wasn't cloaking out before I had to rely completely on my heals (they started catching on started reserving their cloak-breaking powers, but even so, I still managed to hang in there).
Now, the interesting thing about all this is that not only am I not even using a fleet ship yet, but I also don't have the best gear yet nor even any of the reputation stuff.
Yeah, spec'ed and geared right, they're pretty tough ships for the most part. The main trouble is that people aren't used to needing to skill into Starship Warp Core Potential and Starship Shield Performance (which you have maxed) and end up with little shield resist and regen thanks to the lower base power available on the Singularity Cores.
A lot of the early complaining was also not having rep gear yet and using the Jem'hadar or Tal'Shiar Deflector, which do nothing for tanking, instead of going Positron like you are.
Some of it was, and possibly still is on fewer ships, bugs related to cloak, like warp core breaches ignoring shields because the game engine thought you were cloaked (and therefore shield-less, even though the Scimitar changed that) at the time.