How to fight Sombra when she almost instakills?

no, lets give this a try.

If you could block the other team from rotation you would win the game right?

If you couldn’t rotate, you are not taking any points, you are not contesting any ground, you are not even getting to the cart.

And you have a hero which stops rotations by just existing?

That would mean she was a free win, EVERY SINGLE TIME.

This claim of yours is straight up provable to be wrong.

Most of your claims you could make an argument for, but this? no, it is trivial to prove it is false.