the load will only see the lower of the 2,
No that is not how it will work. Everything that MarkT said, plus what happens is that you start to back feed current into the lower supply. The normal current that the load will take will also cause a voltage drop across the resistor to add to the differential voltage. The source impedance of the power supply will be higher and could also cause oscillations.
If you want better than a diode you could use a Schottky diode as these have a much smaller forward voltage drop.
At this point 40 years of actual design in a job seems very unlikely.
Well left school -> two years in industrial electronics -> degree in Physical Electronics (4 years) -> 3 years grad school -> 21 years University Lecturer ( U.S. read Professor ) in Physics / micro computer instrumentation -> 4 Years designing Digital Set top boxes -> 5 years designing RFID systems -> 3 years designing a Trans-modulation system -> 4 years freelance consultant -> supposed to be retired but now writing books. It adds up. 