You are quite right, the risk of secondary transmission was reduced by 79% when the positive case wore a mask AND all the individuals in the house also wore a mask prior to the onset of symptoms, so teasing that apart is impossible. What we really did not understand in the early days was the effect of asymptomatic spread on case numbers, this study seems to suggest that masks are effective in preventing transmission when the index case is infective, but does not have symptoms.
I think mask wearing has become so highly politicised, especially in the US but also in some political viewpoints in the UK, that there is little point arguing. I wont harp on any further but it is really important to bear in mind how COVID spreads, this is a respiratory virus that largely does not spread by contaminated surfaces. We argue about wearing masks while we consume huge quantities of anti-viral wipes and cleaning products.
At the end of the day it is up to Ryanair to decide what rules, conditions or other terms passengers need to comply with to board their aircraft, over and above any legal requirements. Their website makes it very clear (far clearer than many of their other T&C's!) that a mask is mandatory while on board a Ryanair aircraft and they are clear they have no plans to change it. At least they are being up front and clear with passengers what to expect. You can't say farer than that.