I think the error in this thinking is in assuming that the market leader will be the source of the next step change in innovation. This is covered very well in the book "The Innovator's Dilemma". Bottom line, this is seldom the case. If the inflection point in battery technology comes from an outfit Tesla does not control they could be in trouble. All other car manufacturers will simply go off and buy these new better batteries while Tesla will have to figure out what to do with a factory that can't produce them and, perhaps, never will because they won't have command of the tech.