The 5 
CR-90/Ackbar and even the 4 
CR-90 + 4 X-Wing lists have big trouble with dealing with fighters. Rhymer and a few Bomber Squadrons could seriously hurt any of the 
CR-90s if activated via Squadron Command, and the 4 X-wings could easily be pinned by 4-5 TIES or 3-4 TIE Ints, and outright eliminated with a combo of Mauler, Fel, and TIE Adv.
 
 The 
CR-90's though are just going to be very fragile overall. As long as you're able to land at least four dice on them, they'll be hurting. If you've got Admiral Screed with some amount of Gladiators (w/ Concussions or Assault Protons) and/or two Raiders (w/Assault Protons and/or Overload Pulse), you can guarantee some level of critical damage going through almost every time you shoot at them.
 
 My opinion on the 
CR-90 is that it is an objective grabber first and fire-support second. I find them a bit too fragile to use in numbers as a main attack force. However, I will say that if I bring Ackbar in a list, I will bring a 
CR-90A with Enhanced Armament and let loose an unexpected attack on something's rear arc  

 .