Can we think of any time a Vintage-playable effect got legs and was worse? Seems to me every time they do this the effect gets better.
Magus of the Jar? Magus of the Bazaar? Magus of the Moat? Magus of the Abyss? Magus of the Library? Magus of the Tabernacle? Magus of the Wheel? Magus of the Will?
I mean... yeah, but... some of those did not JUST grow legs, they also got material drawbacks. Abyss kills itself. Wheel and Tabernacle and Bazaar and Will all cost more.
The best counterexamples are probably Jar and Moat. With Jar, I guess the analogy is whether Tinker/Shops are so critical to Crucible that it's not good without them in the same way that Memory Jar owes much of its existence to those cards. I'm not sure that one is fair either.
But Magus of the Moat is pretty spot-on as a counterexample, I admit. (I also love Magus of the Moat!)
Magus of the Moat was in Brian Kelly's Championship sideboard.