RJ, if the civil T/R, was meant to be doing sling loading over 50 nm distances it would have been designed with a more efficient rotor system or not designed at all.
That is why the USMC has v-22s and (soon) 53Ks, two different missions.
The 609 has the same powerplant as the 139, however its GW is at least 2000 lbs higher and my guess is the empty weight is around 12000/12500 lbs.
The 609 is designed to fly efficiently, like a turboprop at altitudes requiring pressurization, hence the higher weight for structure.
I don't get your beef, I would not go offroading in a Ferrari and wouldn't go on a racetrack in a jeep Wrangler.
Even with the same powerplant as the 609, the 139 does not go 720nm period. And with 12 passengers you don't carry full fuel and auxiliary fuel, unless you operate at increased gross weights, but then you have compromises in CatA performance.