CR90B and admiral is 69points. If you kill it, you earn 69pts in victory points. Thats the trade. I would quite happily send a CR90A with TRC's or a MC30 to do it, if I can spare them from the main fight.
I don't think either of those can kill it. It can start speed 1, and spam navigates, you get long range, evade most of the damage, you get closer, and its suddenly speed 3 and going the other way and speed 4 the turn after. When a corvette isn't interested in doing any damage, it is very difficult to kill. I personally don't think 'hope the opponent is bad' is a good strategy.
Yes 69 points if (somehow) you kill it, but the rest of the board isn't 320 vs 400, its 360 vs 400. Thats an advantage, but you still have to deal with Rieek.