It is guaranteed arbitrage. There is no risk to the lender, and the only risk to the person that initiated the transaction is that slippage will occur that mak

It is guaranteed arbitrage. There is no risk to the lender, and the only risk to the person that initiated the transaction is that slippage will occur that makes the trade unprofitable, which would cause the transaction to revert, which would cause them to lose the transaction fee for having attempted the transaction. The markets are not currently too efficient for that, and never will be. In fact Uniswap’s entire design depends heavily on arbitrageurs balancing out the markets between itself and other exchanges.