I know exactly what you are saying and I do not disagree. I was heavily into the union side of my last company and I can tell you that pilots will always move on (unless you are happy to sit in the right seat of a BA airplane for 20 years or so to hopefully pick up a juicy carrot at the end). I successfully negotiated a good final salary pension scheme, loss of license insurance scheme and God knows what else but still we lost pilots.
The fact of the matter is that a measureable proportion of your pilot workforce will always have itchy feet. After all, everyone knows that the grass is ALWAYS greener on the the other side.
Most of us have great difficulty in realising that we have actually "ARRIVED".
I ended up after a long career in aviation in a job that I realised was probably the best kept secret in aviation. I was only flying 350-400 hours per annum but, most of it was at night. My mates who were in the bucket and spade brigade (such as Britannia) were flying 800 hours per annum and half of that was at night and their pension scheme was worse than mine.
I never ceased to be amazed at the progression of new pilots. At interview, they would cheerfully kill to get the job. During training (and I usually did the simulator and the aircraft bit) they were as keen as mustard and usually did pretty well. Most of my students turned out well but there was always a percentage that I just KNEW from Day One were going to let me down.
The complainants would usually start after the second recurrent session in the simulator (a year later) and their vision of their perceived future in aviation and their aspirations would have changed somewhat.
And these were the days when the company paid for their type rating. So, as long as pilots are prepared to pay for their type ratings, why should Ryanair lose any sleep?
Incidentally, years ago I was working for a Part 121 operator in the USA. Our ultimate boss was a redneck who had never hired anyone unless they already had a type rating. He had never paid for a type rating course. We persuaded him to run a couple of courses. It was my pleasure to check out one of our British F/Os as a captain in the presence of the FAA examiner (the aircraft was a DC-10).
Two weeks later, the little bugger did a runner and left me and a lot of my friends with a huge amount of egg on our faces having got his qualification.
Ryanair will have no trouble filling their seats for the foreseeable future.