Broadly speaking your instructor is correct, I find that students who have spent a lot of time on a PC sim, generally look inside at the instruments way too much when put in a real aircraft.
A few years ago, I would have said without any hesitation, that they were useless for anything except instrument flying practice, maybe even detrimental for visual flying in a light aircraft.
However the world moves on and now if you have a good graphics package (and a big screen), they may have some benefit for procedural scenarios, looking at nav. routes/features and airport layouts.
While it's great that initially using a sim. has got you interested and enthused for flying, thus eventually into a real aeroplane, so we shouldn't totally rubbish them, used to excess they will usually give you bad habits which have to be unlearned in the early stages of training, which will add to the cost. So I would say your thoughts are pretty much right, lay off the C172 sim. program until at least you've got all the basics mastered in the real world. Good luck and enjoy!