@spook My pleasure. I really do love doing it, and props to these fellas one for doing the real work and making this possible.
As for Missteps, I'm not really sure what it says about how to play or build around Misstep yourself in the micro level. On the macro level, it certainly shows that Misstep makes for this odd prisoner's dilemma, since the more an opponent plays Misstep, the more valuable additional Missteps are for you as well. (Assuming there are any other CMC1 spells in either deck to begin with.)
I think on the micro, level you want to decide what you think your specific Missteps are trying to (mostly) do in your specific deck, amid this play environment where you know opposing Missteps are everywhere. I'm seeing a lot of these decks that are blue and run few or no Missteps (Brian Kelly for example isn't on the no-Misstep list, but he only ran 2) and they tend to be these super aggressive combo style things, ala Reid Duke.
For more defensive hard control deck, I would guess that more Missteps might be better?
A side thought I had is, if people really did want to restrict a card that would balance out Shops decks, I really think the card to restrict would be Misstep. It would make blue decks automatically spend fewer card slots fighting each other, and make the field of non-taxing effect decks have far fewer dead cards game one against Shops/Eldrazi/Hatebears type things. Plus you would see expanded use of things like Dark Ritual/Deathrite Shaman/and Crop Rotation which are pretty good cards yet almost unplayable right now because of Misstep saturation. I feel like, in total, the deck that would be most hurt by restricting Misstep, ironically, would be Shops.
Full disclosure, I'm not saying that all should happen, only that if Misstep was restricted that I'm pretty confident those would be the effects.
I'm torn. Out of principle I don't think that Misstep should be restricted (because it's clearly not overpowered), but on the other hand I think that it would be very good for Vintage if it was.
I also don't entirely agree with your assessment. From a theoretical point of view, the shorter the games go, the better Misstep is. Reid Duke's deck doesn't care too much about opposing Missteps, so that's why it's not needed in his build.