Can only speak for Luton base, but you would be hard pressed to find any cadet or ATP FO's with greater than 500 hours that aren't waiting for a course date, sim check or interview with BA. Brand new TRSS FO's are also on their way out the door, taking their type rating and debt with them.
The issue is with easyJet, not CTC. Until conditions are vastly improved, all flight crew, from day 1 cadet to training captains will be leaving for companies that offer a better lifestyle (notice lifestyle being the issue, not pay).
Not sure that anything could be written into the contracts to keep cadets from leaving. You are applying to CTC, not easy. As a cadet or ATP, you are placed with an airline. You couldn't lock someone into easy for 7 years while someone placed with Tommyfly or Monarch was free after six months.
Best wishes
Buter