I recently bought the Chinese cnc3018 Pro with a 450nm 3500mw laser head. In some places I saw it mentioned not to run those laser heads at their max power because it will shorten their lifespan significantly.

My question is, is there any truth to this, or is it just being overcautious?

The module takes 16.8W of electrical power. If the fan uses 1W the remainder could well be explained if it contains a 3.5W (15W electrical) diode.