I concur with all you said, I just don't see how this is backing your former critique of Celtic or Germanic groups and languages. Reconstruction of old languages is a retrospective method, so if there was no big movement of people (as far as this can be judged from archaeological findings) and we have certain languages then and now, how do you argue against the common scientific approach of reconstruction and labeling certain groups with certain names? If you only liked to say that we have to be extremely careful not to overestimate the possible (speculative) correlation of certain archaeological groups with certain language groups or ethnic groups, ok.