9 times out of 10 "bro's" will talk about shit they don't know about just so they fit in or sound knowledgeable...
T3 simply increases your metabolism exponentially. There is no sweet spot, only preferred dose based on individual goals and tolerance of side effects.
Can it peel muscle off of you? Absolutely, if you let your body fall into a catabolic state just like any other time except at a greater rate because your taking powerful medications.
That's why it is suggested to be taken with something anti-catabolic (aas) so as to prevent that muscle wasting from happening.
With that said, you could try to play with small doses to see what works for you, but your planning on doing this naturally so it isn't advised.