It would be interesting to see how compatible the MRH is with the opv80. Even so the MH-60 is much more probable.I dealt 600kg will make much of a difference. Has been my experience in life that such limitations dont actually give an accurate representation of what the device can perform but rather it being a safe number put in place to keep the lawyers happy.
Should also note that the 10.6 ton of the MRH is for a fully loaded aircraft, with 4.2 ton of fuel, persons and cargo, When operating from an OPV I can imagine any scenario that would require that max load out.
But realistically these are likely to be embarked with smaller aircraft. UAV's etc. The EC135 could be embarked as a light utility helicopter.