Uniswap (v2) has simple contracts, has been audited multiple times, holds billions of USD and it has not faced any kind of systemic attack. The only issue that I can think of is that pools with low liquidity can suffer from front-running.

Even the fees are not a "problem", if you consider that there are already roll ups (loopring, zkswap) that run pretty much the same version of those contracts and cost fractions of a penny.