Having used both LGW and LTN extensively over the last year, I can definitely say delays are not the same between both airports, although that said I think FR do a far better job in scheduling than EZY; one captain of the latter once described the schedule as "optimistic" - the former do seem to pad out back at base.
LGW squeeze every second out of their runway and fair play to the controllers who manage this - but one small delay has potentially long knock on delays. In comparison, it's rare to even have to go into a hold at LTN. If LTN goes up to 30m+ a year, delays will increase.
You can't do the third trip of the day, in the summer season on simply 40 minute T/As or less. It doesn't work - one small delay knocks on for the rest of the day. Add in a stormy day with reduced flow rate into London TMA and aircraft just can't get in without having 1-2 hour delays if you miss the slot even by a few minutes. EZY at LGW must have cancelled 1000s of flights over this summer.