Aside from everyone marking their own meetings as IMPORTANT! you could also delete all meeting requests that are "flexible" or deemed not critical - why are they being held in the forst place?
We think of priority based on time sensitivity - not importance. For example, if I have a 1:1 with my direct report, it is very important but not time sensitive. This allows us to move that 1:1 if needed to accommodate a more urgent meeting
