Has there ever been a more useless convention than “On your left” (or right) when passing a pedestrian or slower bike? Nine times out of ten, the passee just goes in the direction you just hollered. It’s human nature! You hear “left”, you move left.
But not always, so you can’t rely on it and do the opposite.
Stealth passing doesn’t work as people are herd animals, and like cows and sheep, wander all over the road randomly. Unless it narrows, then like cows and sheep, they’ll stop at the chokepoint to mill.
Slowing doesn’t work, because it just increases the cross section with the person (or dog) – the more time you allow, the more likely they are to veer into your path. The trade-off is to go faster and get past at a lesser risk of a high-speed collision, or go slow and increase the risk to inevitability of a low-speed collision, and the inevitable unpleasant confrontation with the person wandering all over the road like a locoweed-affected bovine. If you go fast you leave that in the distance too.
I can’t think of a better one though, and neither can anyone else, so we’re stuck with it.