Congrats to the brave Painter innovator who only played 2 Missteps (granted he's maining 4 blasts :p ).
I'm not fond of misstep at all. None of my decks have featured 4, 2 or 3 are the mean and as you say, playing blasts is less useful (and 2 snapcasters can recover them).
Besides, why should I want 4? To protect ancestral? I cannot fetch it, so in most games i don't see it. To protect grindstone or top? People rarely counter grindstone as it's a dead card itself, and while top is great, playing magus means i cannot fetch (removing all options to shuffle my deck).
Which cards would I counter? Stp, for sure, but it's on the low. It's dead against MUD, poor against dredge, mediocre against fish variants or heavy control. There are 23 preordains among other 15th top decks, averaging 1.5. I can be totally wrong, but I hate dead cards and I already play a bunch. I'd play 5th blast over 3rd misstep unless delver was heavy in the meta.