If every unit in Europe was fully staffed then the Flow Management Unit in Brussels could shut up shop. Their main function is to redirect traffic from sectors that are overloaded, for whatever reason, to sectors that can take up the slack. When this is not possible the traffic gets delayed before departure until the sector capacities en-route can cope.
So, if you want to know if there is an ATCO shortage anywhere in the world you just need to look for the delays. Because, delays equal staff shortages. The big worry is, are delays increasing or decreasing? My guess, based on my own travel experiences in the last few years, is that delays are increasing. How many times recently have I been told over the PA that "there will be a delay to our departure due to ATC", for whatever reason?
If the ANSPs think that they are adequately staffed, then our friendly "journos" should be asking them what the cumulative delays are at their units.
My own guess is that once cumulative delays amount to in exess of one hour per flight then there will be public pressure for a massive ATCO recruitment campaign. Then again pigs might fly!