Try departing or maneuvering over a high-G Planet (especially one very near a Sun)

Then you'll see what Clean Drives are really worth.
Not many Ships are really that heavily affected across the board, though. But a Lakon Type-6/7/9 or a Beluga with their very poor Engine heat tolerance will benefit quite a bit.
Other than that, it's true of course that any Drive Tuning increases power Draw and thus heat a little bit.
But moving the Throttle forward (i.e. on above Ships) easily generates 10x more heat than the miniscule heat added by Power Draw (actually also in SC).
And that's where Clean Drives come in very handy if the Ship suffers from Engine-related heat issues.
The ones where the Engine puts them beyond their Heat Envelope can quickly be identified by charging FSD and additionally tapping Afterburner (simulating an escape jump).
Most Combat- and Multirole Ships have little or even zero issues with doing so. Alot of other Ships however, can literally cook off just doing that. Those bascially are the primary Clean Drives candidates.