There is overlap in some of these walkers to the point where the first of walker B is likely better than the second copy of walker A, so I suspect you may see more cards with fewer copies in vintage. I would much rather be in a situation where I have some combination of Ashiok, Teferi, Dovin, Narset, or Shaeeli in play than having redundant copies in hand.
I do like that this card does not care where the effect comes from, so it turns off your symmetrical effects like Howling mine, not that it sees play in this format but its going to be great in my turns list in modern.
This does just put JTMS in his place, and supports your other walkers static effects by preventing you opponent from seeing new cards outside of instant speed stuff on your turn like Opt. If the worst case situation is that this comes down, impulses, and then make your opponent deal with it, it is probably already worth it.