some led bulbs do get hot... but the cooler they run, the longer they last.
why would you want or need to run both masthead lights at night?...
if the fixture is an approved device, it has been tested to work dependably with either one or both "bulbs" glowing at the same time in many different conditions.
I can see that a redundant mast light could save an unplanned trip up the mast to replace a bulb, but with led its unlikely that you will ever need to have redundancy, but if you are running them both, it will probably go unnoticed if one quits... then there will be no redundancy..