My own long term experience is that any board mounted component that has a surface temperature of 80C will blacken a board over time.
That is not temperature rise, but absolute surface temperature.
Resistors must be greatly de-rated, If the resistor is specified as 25 watts dissipation at 250C rise, something like 3 watts would be realistic, giving 30C rise in a 40C ambient.
That 70C would still be capable of leaving a painful burn on the tip of your finger at 3 continuous watts.
It would still need to be mounted on ceramic spacers above the board,and be through hole, and have very generous pad areas.
The ceramic beads pull an amazing amount of heat out of the leads, and provide much more surface area so the solder pad can run much cooler than the resistor body.
Anything much bigger than that needs to be an aluminium clad resistor bolted to a heat sink.
My own "rule of thumb" for designing ANYTHING, if I cannot hold my thumb on it indefinitely when its running absolutely flat out.
It gets redesigned.