His final stance has a timer on it and by the time you get DP out he might be out of the stance and has to build his "case" back up.
And Magneto's LVL3, which has no prerequisite to it kills, Phoenix in 1 shot with his LVL3. And it hits everywhere so Phoenix has to think twice about pressing a button. Hawkeye too his LVL1 hits everywhere and is instant plus can be linked together.
The DP era has pretty much ended or at least she isn't going to be a dominant force in tournament anymore. 90% of the system wide changes in UMVC3 were made to nerf Phoenix. Nerfed X factor scaling/damage, decreased timer on XF, TACs changed up, meter gain reduced, snap back duration increased, raw tag ins no longer hit overhead, Phoenix herself nerfed, characters given meter stealing moves and other stuff.