If buying at X and selling at X + ε is "arbitrage", every retailer is merely "arb-ing". Even looking at the definition you gave I don't think it pass the smell

If buying at X and selling at X + ε is "arbitrage", every retailer is merely "arb-ing". Even looking at the definition you gave I don't think it pass the smell test, the scenario does not require the buying and selling to be simultaneous... not in the ice cream analogy, and much less in the real uniswap mechanism.