Have you booked your flight yet? if not then I would strongly suggest that you avoid ryanair.
we had some clients this summer flying from london to salzburg/munich with ryanair and the number of damaged bikes was much higher than with any other carrier. they also put a dent in one of my own bikes… I travel regularly and know how to wrap up my bikes, so they did an impressive job in denting it. I’ve flown a few times with easyjet and they seem to be much more reliable.
As for the weight question – could you not pack your panniers into a bigger bag, then just organize it when you get there?