I agree you can compare them but you can not blame the low costs of Europe for having higher restrictions than the US when they have higher operating costs.
Comments like:
"which leaves that cr@p outfit RYR out"
Must be justified, it's an unfair comparison.
From my own experience the 15kg limit for Ryanair and other low costs is a reasonable limit for the price of the ticket.
An average by European standards case weighs 15kg at check-in.
So would you argue that it would be justified to increase the ticket prices across the board to accommodate the small minority who travel with 31kg of luggage? Rather than charging the majority less and minority more.
Take less pay less, take more pay more.
Fair in my book.