Lower Score in Coliseum after Unlocking Marquee

Remember that your summons are given the AVG level of your unlocked & levelled toons. If L31 is less than your other toons, it will hurt your summons, not help them. 

As for the rest, the Coliseum is fairly RNG sensitive. It's not so entirely RNG that I can't beat my old score in 5 tries, but it's random enough that it's rare to beat my old score on the first try. Those AoEs are pretty brutal. 

I'm with you on CG needing to recalibrate, but there are things you can do to make things better for yourself.