Power Ratings of RF Attenuators In Series
A 2W attenuator is not designed to dissipate 2W, it's designed to receive 2W.

The amount of power at its output will be determined by its attenuation. A 3dB attenuator would output 1W. A 10dB attenuator would output 200mW.

If you cascade attenuators, each attenuator only needs to be rated for the expected output power of the previous one.