A three bladed prop modification along with floats is very common. Wipaire, the leading float manufacturer has its own STC for that. In combination with STOL kits is not uncommon either. I expect the Robinson STOL STC explicitly accommodates floats (Wipaire’ STOL STC sure do) but not sure since I don’t have the paperwork in front of me.

You are over inflating issues here. Are you a pilot? The issue here is straight up incompetent operation of an aircraft.

Operating a floatplane and separately operating with a STOL kits can increase complexity and risks especially when aircraft are mishandled/abused like here with an incompetent pilot who does not know what they are doing. You don’t need to dream up issues from combination of stuff here, the simple linear addition of issues was more than enough for an incompetent pilot to get into trouble, and seems they are lucky they did not get into more trouble before, and lucky they were not killed.

The C185 is a beautiful well behaved workhorse used extensively in bush and floatplane flying, often with multiple STCs to upgrade these aircraft.