Heat is the way incandescents work. If they didn't get hot, they wouldn't make any light. Heat "degrades" them only in the sense that heating them (i.e., turning them on) eventually uses them up. The filament reaches temperatures of 2,000+ degrees C a fraction of a second after it's turned on; the type of fixture the bulb is in won't change the filament temperature much.

Filament resistance goes up because it is evaporating, heat goes up because the filament increases in resistance.

Higher overall resistance connected to the same voltage produces less current draw and therefore less heat. It's just Ohm's law.

The filament doesn't thin out uniformly, it tends to develop localized hotspots which leads to accelerated, localized evaporation. Eventually it breaks.

I have a 60W bulb I run through a dimmer that is in its 4th year.

You can make an incandescent bulb last an arbitrarily long time if you're willing to sacrifice efficiency by running the filament cooler. A dimmed-down 60W bulb may produce the light of a 5W nightlight bulb but use far more than 5W.

The Centennial Light Bulb has lasted a long time, not because it's never turned off, but because it's absolute shit as a light source. The filament stays cool and as a result its both terribly dim and terribly inefficient.

http://www.centennialbulb.org/

> Heat does degrade incandescents.

I didn't say heat didn't degrade incandescents, I said LEDs are much more heavily degraded when they're over their heat capacity.