I can understand safety must come first.
If slots can be avoided then, as a passenger yesterday, may I illustrate why.
PIK - Dublin due to depart 0915 was held on the ground for nearly an hour, then travelled. Not a big deal.
Dublin - PIK due to depart 2115 departed at near 2300, landed 2345 ish, and returned then to Dublin. A Dublin based aircraft doing its last rotation of the day.
If these Dublin based delays continue, how close does it get to that final rotation of the day being cancelled ? That is a big deal, because we all know what happens when our favourite airline cancels flights !