Besides that, centralized exchanges have greater performance than Blockchain-based solutions (like atomic swaps, decentralized exchanges, etc). Decentralized projects will never be able to compete with their centralized counterparts because of the huge discrepancy in performance. Traders want something that's fast, secure, and cheap in order to maximize their profits as much as possible.
It depends on the use case. You may be right about for-profit traders who need a high performance. But for people who simply want to exchange BTC for LTC for example, a single time, and thus do not depend on a fast trading performance, atomic swaps can compete with centrally managed exchanges.
An atomic swap in this comparison has often a competitive advantage because a CEX depends on charging a fee (otherwise it would be unprofitable) while an atomic swap does not. There are of course situations where the transaction fees needed for atomic swaps are higher than a typical CEX fee. But this is only a short term advantage, because a CEX will also need to adjust its deposit/withdrawal fee if the on-chain transaction fees are too high to cross-subsidize it. For example, Bitstamp for a long time cross-subsidized the withdrawal fees until it was forced, because of rising average tx fees, to charge a withdrawal fee.
A disadvantage of atomic swaps is the inherent optionality: one of the both traders can opt-out for a certain time. But this problem can be minimized with short timelocks and it can be "productively" used to create option contracts.
With new scalability solutions such as The Lightning Network, and sidechains, it may be possible to obtain all of the benefits of centralized exchanges in a decentralized project.
I guess a centralized database will always be faster. But for trading strategies that do not depend on front-running (trading-bot strategies that depend on being faster than others) a LN-based atomic swap exchange may suffice. So I guess in the end DEXes can get a big market share but there will always be a big share for CEXes, too.