My understanding is that RPT <15,000 kg MTOW pay NO enroute Nav Charges (something to do with Regional Area susbsidy - JA's voter base for the cynics like me) - this is not funded - and the big winner is the QF subsidiaries.
If what you write regarding MTOW is correct Uncommon Sense, then the QF subsidiaries win nothing - zero. The smallest Dash 8 is 15.6 tonnes MTOW and the largest 19.5 tonnes MTOW.