Wizz needed to do this because they were getting hit more than Ryanair due to the situation at Modlin, as they base quite a few aircraft at WMI and don't have much slack in their fleet compared to FR. With FR not having a base at WMI it is much easier to direct aircraft elsewhere and operate them from Lodz or Warsaw without mass scale disruption.
What they did with me a few weeks back is that my flight from WMI to DUB was delayed by a few hours and operated from WAW and they transported us all up there. The same DUB based crew were set to do a couple of other flights that day, short ones I believed, but they both ran on time as another 737-800 and crew were drafted in to do the rest of the duty.
With Wizz they have the problem that almost all routes from WMI are using Warsaw based crew and planes, some of which have been stuck on the ground for the whole day and all of the routes are to non based pretty much apart from Budapest, also with by far less spare aircraft free as they are not grounding any during the winter, it's very hard to keep diverting flights and it not badly effecting them. The fact that pretty much all W6 flights from Warsaw are WMI crew is the biggest problem for them.
Generally what has been illustrated the past few days is that Wizz have cancelled a higher percentage than Ryanair, who appear to not cancel anything from morning to mid afternoon. But most of the Ryanair late flights are the ones that seem to be cancelled, I know that during the full days of disruption, the availability of buses in the afternoon has been a problem as well for both FR and W6.