Why would the gains be exponential? Assume that X "first arrival" develops a model with a certain rnd investment, and Y arrives next year with investment that's an order of magnitude less costly by following, and there's a simple enough switchover for customers. That's what's meant by no defensible moat; a counterexample is Google up to 2022 where for more than a decade nothing else came close in value prop. Maybe X now has an even better model with more investment, but Y is good enough and can charge way less even if their models are less cost-effective.