The system works well or not depending on the restrictions set by the company and based on how many days of holidays are made available.
I have never had problems to get holiday in easyJet.
When I was on a fixed roster it was enough to get a block of 5 days of leave to get 13 days off (4 off/5 lve/4 off). Getting two consecutive blocks of leave in the summer is not easy.
Of course if you want three weeks in August it might be difficult, but I have managed consistently getting more than a months off in low season the last couple of years.