That holds (? used to hold?) true from anything to GPUs to individual capacitors, the repetition of the heat cool cycles is the primary cause of wear.
I'm not sure whether constant running is worse for wear and tear vs power cycling but power cycling is typically what precedes a failure.
This isn't true at all.
That failure mode is more, it works fine when initially turned on, then starts failing/flickering on and off once it has gotten to temperature.
Also in this case we have mechanical components under constant usage (fans), and the effects of long term heat on the thermal compound between the die and cooler plates to consider.