Wouldn’t agree.
You could’ve recorded a 30 minute video with the flashlight on without any issues. They also wouldn’t allow API access to the flashlight hardware for those apps if it was damaging the phones.
Plastic Sony Ericssons and Nokias had flashlights circa 2005 and could shine day and night and every one of those phones had internal power control of the LED (it would shine brighter when taking a photo and be dimmer when used as a flashlight).
Meanwhile metal and glass iPhones with even better heat dissipation didn’t have flashlight as a system feature until iOS 7 in 2013.