Lens is very strong but it only "shuts down wizards" if your list is only wizards.
Tzeentch say hi....
Plus, generally speaking your army has a certain focus due to synergies. E.g. our skink armies have wizards at their core as heroes. Swapping one of em out for a saurus is fairly pointless if you want it to actually synergize.
It invalidates pretty much all of that. Or well, hits those tactics rather hard.
Anyways long story the idea behind the artifact, a protective bubble against damaging spells, is fine. However, this incarnation has several issues.
1) It's too reliable, working against all spells & guaranteeing to block at least 1 damage.
2) It's too powerfull having a 66% chance of completly negating about 90% of all offensive spells in the game. I mean it's frequently going to be better than trying to unbind which is supposed to be the main anti-magic mechanic….
3) It turns any hero into an anti-wizard character at very little cost or effort.
4) The wizard has nothing to respond with (calling in friends still leaves the wizard to stand around looking pretty in the best case scenario while waiting for the carrier of the artifact to be pummeled by his friends...)
Better variants of the same artifact would be the following:
1) On being damaged roll a d6, on a 4+ block damage, significantly reducing its reliability
2) Block damage to a minimum of 1, guaranteeing spells still do
something even if they are significantly less effective.
3) Limiting the amount of spells it can block (e.g.; it only blocks the first spell each turn, or after blocking a spell there's a chance the artifact breaks)
4) Give wizards significantly more tools in their base-kit so they can actually choose to do something else when their destructive spellcasting gets neutered by the artifact.
All of those would still make for a powerfull anti-wizard artifact but give the wizards some options to actually respond with thus being far better variants. And that's just the variants I can think of quickly of the top of my head, there's bound to be more that'd avoid completly breaking wizards while still being more than powerfull enough to be good anti-wizards artifacts.