Why do you think gate agents approach the rule "pragmatically" (i.e. disregard it), and allow you to bring into the cabin a bag which is larger than what is allowed? Because the rule is crazy, and they know it. If it wasn't crazy, they would just follow it. How else would you call a rule which is consistently ignored by the people who are supposed to enforce it? If you don't like crazy, we could perhaps agree on idiotic?

There is no point in discussing this particular aspect of Ryanair's cabin baggage policy further. Safe travels.