I agree that there should be one and only one protocol, and ADS-B seems to be best indicated.
A viewpoint presumably based on the type of aircraft you fly and how you fly. The transponder and ADS-B technologies are percolating down from the commercial aircraft world where electricity is abundant, being within 5 miles and 1000’ of another aircraft is too close and speeds are high – up to 250 kts at any level outside controlled airspace.
GA includes balloons, (airships?) parachutists, gliders, hang gliders, helicopters, aeroplanes, paramotors, UAVs etc.. Why assume that what you want is appropriate or even practicable for all other airspace users. Some categories of aircraft (I guess a parachute or paramotor is an aircraft?) routinely fly in close proximity and don’t even carry a battery. If ADS-B did not already exist a technically superior solution would be devised using the best bits of e.g. FLARM as well as transponder technology. For sure a modern solution would not need the maximum permitted ADS-B peak transmit power of 500 Watts. FLARM works on mW powers and ground receivers can receive at ranges of up to 30 km.