Yes, it is true that it is much more difficult than in the past, at least for well-known methods described in the literature. But it still works, if you are smart.
This is why we run our own research to find methods still having some edge.
One thing I can already recommend is to look at pairs traded in a single direction (long only, for instance). Like one direction stat-arb pairs based on one stock and one ETFs. Trading pairs like this is not really described in the literature much.
Example here:
https://www.pairtradinglab.com/backtests/Vdrn5bhwpZRml5vlThis is an arbitrage between Sherwin-Williams Company and an ETF fund. Long positions opened only.
Also what you have read usually applies to US stock market only (they often don't consider ETFs in the literature). There are also many opportunities in other stock markets (LSE, Singapore, Indian stocks, ...). PTL platform will support more markets in future.
If you are a small retail trader, you may want to try pair trading stocks having just enough liquidity to be tradeable by yourself, but illiquid to be traded by big players.