this change ins very noticeable as soon as ATC / weather issues are predicted or known about as you rightly say EZY take an axe to their third wave.
this sometimes turns out to be a good decision and sometimes it’s OTT if issues don’t manifest themselves as expected.
but being preemptive and canx say 20 departures early enough means circa 3,500 fewer pax to have to manage/decontrol etc if it all goes wrong late afternoon/evening and removing these flights adds to the operational resilience of the flights that are left.
23rd October 2022. A date etched in my soul. A storm cell sitting over Gatwick for hours. I arrived at at 17:00 hrs to see pier 5 full of aircraft loaded with pax and and bags, jetties off, waiting to go. Crew rapidly running out of hours. Then the cancellations. Total carnage. Passengers off, planes towed to remote stands to allow inbounds a stand. Bags still on them. Thousands of offloaded pax waiting 5+ hours in baggage reclaim, taxiways blocked by aircraft awaiting a stand.
Offloaded baggage was nothing to do with me, but the "big" boss at the time asked me to go and talk to the poor passengers waiting for their bags, as I was closest. The subsequent 3 hrs of justified abuse was the catalyst to my decision to leave. I don't mind being called an "f.....g c...t" as it's probably true, but the spitting was the final straw.
Cancelling some of wave 3 helps, however it is usually too late for a lot of passengers who are en route/already checked bags in. When you suddenly get a list of 25+ flights that are cancelled, all the bags already checked-in have to be returned to baggage reclaim. I had barely enough staff to sort the outbound baggage, losing 3 or 4 to return cancelled flight baggage was a kick in the teeth.
200+ departures a day for U2 is fanciful at best, downright negligent in reality. U2 and LGW got greedy, writing cheques they couldn't cash.