I wouldn't say Clevo cooling is inherently good out of the box. They use beefy fans and heatsinks to compensate for other design flaws. Lots of units ship with warped heat sinks that need to be lapped and on many models, the bottom case vents are extremely restrictive. Cutting mine out literally reduced temps by 10C across the board.
If you fix these issues, then the cooling systems in Clevos are beastly. Can't comment on newer alienwares, but older ones had fantastic cooling systems too.