So far the only exchanges where I found some opportunities are the ones that do have a public API, probably because there is less competition on those.

For example, I have yet to find a single profitable pair loop on Binance, despite parsing their WebSocket feed.

But on exchanges that implement anti-scripts, it is not uncommon to have pair loops with a ±1% profit after fees. The hassle is to implement trading with tools like Selenium to proceed with the trade.