Actually, Max's article is a devastating argument against the case for restricting Misstep. Restricting Misstep will just replace those slots with other cards that are bad against Shops, so restricting Misstep will have no net effect on Shops.
Restricting Misstep won't make Shops weaker in the metagame.
If Missteps get replaced by Pyroblasts, that indeed will have little effect on the blue-vs-blue match, and also on the blue-vs-shops match. However, there can be effects on other matchups that can theoretically have cascading effects.
Misstep differs from Pyroblast in that it has utility against non-blue decks, some of which might match up favorably against shops. For example, Vintage Lands. Restricting Misstep could make a deck like Vintage Lands more playable, which could force shops to devote more sideboard slots to that matchup, which could weaken shops as a whole.
As it stands, shops decks are effectively able to pack hate against Vintage Lands without using up a single slot in their 75. Instead, they are packing the required hate in the 75 of their blue opponents.
Vintage.. Lands!? Well, since that deck couldn't be any less playable than it already is, I guess you're right.
The only thing restricting Misstep accomplishes is that even more start playing red in combination with blue than what we already see right now. Color combinations like UWB will get pushed out in the dark.