Wanderer has the same problem as old Variax, It is perfectly fine if played on curve but it gets out of hand if when it gets ramped. Possible solutions include the Variax treatment i.e. increasing its cost (will quite possibly kill Wanderer for factions without ramp), Nerfing its stats, and simply making it unrampable. I personally would prefer the last option but I doubt that will happen.
As for countering Wanderer there are actually quite a few ways to do that including Artifact decks (One-woman army Reva), Aggro and Burn decks, Decks with better lategame than Wanderer that can reliably achieve said lategame (Fault) and lastly decks that can Snowball/out Tempo Wanderer (the only decks I’m aware of that reliably do this are Pantheran Vet and Arcanyst decks). The main problem is if you can’t abuse one of Wanderer’s weaknesses (which almost every midrange deck in the game cannot do) he will just steamroll you with Statsticks.