Perhaps it would be helpful to make clear in which state each character is in.
The most reasonable assumption is, that they are all in the form they were during their time in this teams.
-Iceman is not made of ice yet and shattering would kill him.
-Jean has only TK.
-Quicksilver is at about mach1.
-Polaris is not trained by Magneto yet, thus not able to manipulate the bloodstream.
-Havoc and Scott are on the same powerlevel.
Now discuss again!