There's two distinct categories in Thomas Cook. The new guys who having come from some, comparatively speaking, bad places to work and those senior captains who started flying in the 80s and early 90s who have seen things to be a lot cushier in the past. Amongst the newer population of pilots, most people are very happy indeed. Ts & Cs are comparable to BA, almost everyone is in the base they desire and rostering works in tune with a scheduling agreement that would give MOL and McCall nightmares.
There is a seniority list, yes. We will have hired about 150 new FOs since Jan 2015. About 50 FOs waiting for a very long time for command (>12 years) have been promoted to Captain since then and appox 50 more upgrades due this year. They are working through the list thick and fast with some saying those who joined in Jan 2015 might be up for an opportunity within a year or two (a lot don't even have the hours!)
Recruitment has now ended for 2017 and in the next few years we will be focussing on cadet recruitment in the main to address what might otherwise turn out to be another age/experience problem (too many highly experienced FOs waiting for a command).
Hope this helps.