I find it hard to believe. As you yourself wrote: “I cannot imagine any rav telling a person that this is assur, unless the question was framed in a way that could involve halachic issues, like lifting weights on SHabbos, or in a mixed environment for someone who is sensitive to that.”
IF anyone thinks that it is an ISSUR GAMUR to lift weights, it can only be because of the context – both the individual and the individual situation.
Therefore, I can’t see what the purpose of this discusion is especially since I don’t think it is relevant to any of us currently involved in it.