There is a balancing act on the fees, charge too high and people won't forget, hence regular ticket prices must go up to make for lost revenues, charge too little and you must raise ticket prices to make up lost revenues. Problem for Ryanair is that a large part of their revenues come from those fees, so much so that if you were to remove the fees all together, Ryanair would be loss making.
Afraid that is plain wrong.
Numbers not checking in online is minor.
Ryanair earn 1/4 of revenue from add ons and that includes Insurance / Food / Luggage / Car Rental / Bus Tickets / etc etc Prob Food / Car Hire and Bags are major part. I see little chance in % of revenue.
Having got off Ryanair flight at Shannon about 6 years ago and made way to Hertz office after collecting buggy, no other flights in but 16 people pretty much all off same flight in front of me give an idea of how important it is to Hertz.