Whatever Mauer was has no bearing on who he is (as a player) today. That kind of induction will not fly. I see nothing wrong with the OP's propositions or conclusion given that we assume Mauer is both correct about his self-assessment of his concussion and is telling the truth that he has no lingering symptoms (of course some may be latent so that's what I mean about being correct in his own assessment). If that is the case then the other factors are promising causes of his diminishing ability. I don't see why this is is controversial, other than no one wants to see a super star fall from self-inflicted "coulda, woulda, shouldas." My guess is that it's both concussion and age related, which (if true) makes not keeping the rest of his body as fit as possible a fair target of concern, to say that least.