As said before by Rove (who engineered two POTUS election victories), the only thing that’s important about picking a VP nominee is that the POTUS nominee doesn’t screw it up.
If someone thinks that a VP selection will help win certain states, please refer to:
Bob Dole ‘76
Lloyd Benson ‘84
Jack Kemp ‘96
On the one hand, you and Rove are absolutely correct that the most important factor — by FAR more than half the pie-chart — is the POTUS nominee, not the VP.
But I think you overstate it when you say the VP doesn’t matter at all, or, at least, can NEVER matter. Yes, there are plenty of VP-pickings that were made in hopes of this or that benefit, which didn’t pay off. That doesn’t show that the VP can’t help a little around the edges in some elections.