I also have a 4% card, which took a good amount of effort, and needs regular attention as the issuer has realized it wasn't a good idea and is changing the deal. Now it has a limit and then falls back to 2%. Probably still worth the effort.
Miles/points seems like a lot of work though. I could see a study showing that's not worth the effort for most people... but I think the thing there is to find a card with points that are valuable for you and then maximize that, so there's not a one size fits all there.
Some years ago I looked what my bank offered and there were a lot of exceptions, it was very far from "everything". I think the math came out to saving like $100 total a year, not really worth it.
Anyone who gives a 3% discount for cash will get cash from me, but I already have all my money in index funds. The effort to maximize points is “use this credit card, get the cash back”.
It’s really not that much effort, for rich people with excellent credit. It is of course a hugely regressive system, but that wasn’t the argument you made.
Still wouldn’t recommend them for anyone who’s not particularly good with money, but 2% back for almost no effort is a pretty good trade-off. Keeping track of rotating quarterly bonuses? Yeah—-then it’s worth thinking about ROI of your time.