If Bridge were originally the way you've modified it, I wouldn't have another point of comparison.
You describe a way you beat NV-Bridge. Well, does it consistently beat NV-Bridge? And if so, wouldn't constant attacks also beat down KC-Bridge?
Unless you make every single card the same, there will always be cards and combos that are simply more powerful than others. Should they be removed or nerfed? Sure, if they are so game-breakingly powerful that they are almost always dominant. Bridge as it is simply doesn't fall into that category, so a nerf is not necessary. But leaving it as is means that, in a few games, that combo DOES come up, and then you have a glorious turn where you pile drive the Provinces. That kind of moment is worth having once in a while.
As for [5 cards] + [1 action] = Win...
Well, KC-Goons-Masq pins do that, don't they? Except instead of one glorious megaturn, it is a long and painful grind towards an inevitable conclusion.
But the point is that, in Dominion, you don't just get those 5 cards in hand. That's not how it works. You have to buy KC, and KC is not cheap. You have to align five cards in your hand, and that's not easy either. Treasure Map only requires two cards to kick off, but that in itself is tough enough that it's a weak card. 5 cards is much more difficult.