Ah, but the difference is that tinkering with mixture to optimize the effect of carb heat has been demonstrated to produce quantifiable and desirable intended results toward an objective. And, any undesired affect can be instantly reversed. Not so with flap extension in some aircraft.
Tinkering with the flaps is evidence of a poorly executed approach, in why was that much flap extended so far back on final - it's just evidence of poor airmanship to find yourself in that situation. If you are flying a Twin Comanche, or Navajo, you'll probably get your knuckles wrapped by the check pilot if you start reducing flap extension on final approach, and certainly in any RG airplane you are increasing the risk of a gear up. ('Cause if you get the gear up, rather than some flap, the plane will feel somewhat similar).
On a checkride I once flew in a C310, I retracted the flaps on touchdown. The check pilot told me that he was going to fail my ride for doing that (inducing risk of gear up). I pointed out where it was a Flight Manual procedure for doing that in the 310. He grimaced and could not fail the check ride, but he still took points off.
For checkrides I fly, I would not sign off the pilot if they did, or thought they needed to retract flaps during a continued approach - more training.... = more $. On that same checkride, if the pilot demonstrated the understanding of the systems to know that leaning with carb heat might improve their situation, I would comment their systems knowledge, and broad thinking.
In a C 172, I cannot suggest that retracting the flaps on final is immanently life threatening, but it's an unnecessary and bad habit, which will have to be unlearned in "bigger" flying environments - so why start?