MCH's Wildfire burst is ping sensitive, as it's a fixed 8s you need to cram 5 1.5s GCD's into while weaving. However MCH has a low floor and high ceiling, you can get a decent amount of damage out of it even at sub-optimum performance.

DNC I'm not too experienced with, it doesn't have as strict a burst window, but it can be busier with more weaving, depending on the RNG. I'm not sure if the dance moves themselves might be delayed by high ping, which might cause your Standard and Technical steps to drift out of sync I suppose.
Given DNC's low personal dps, getting your dance buffs out at the right time is crucial to your damage contribution.