This would be like saying "If his Mewtwo hadn't been Specs and instead Life Orb he would have won" or "If his Mewtwo had been Contrary instead" as some sort of justification to ban or not ban the opposing Shadow Tag. Just because things have poor match-ups, such as Magnet Pull vs a team with no Steels or CFZs without Mold Breaker(-esque moves) vs Sturdy Shedinja or Water Bubble vs Desolate Land, doesn't necessarily mean they're not broken. (Or are broken depending on context.) Even among broken and unhealthy stuff, very little, if anything, is literally useful in every possible match-up.I know bb. Just hi-jacking your post to use it as an example for others that are calling for magnet pull ban.
...plus, that kinda logic can be a bit dangerous since one could easily use it to pull some bullcrap like "Well, if his Groudon had been Wonder Guard it still would have been useless in that match, so Wonder Guard isn't broken."