In a fluid there is gravity exerted so we know that the lower layers have higher pressure. Does that prove that Pascal's law is wrong?
Not really. A better expression of Pascal's principle would be: Any externally applied pressure will be transmitted equally to all parts of the fluid.Pascal's principle says that an incompressible liquid in a container exerts the same pressure at all its points.
If you exert a pressure at the top of the tube, the pressure at the bottom of the tube will increase by the same amount. (This is in addition to the hydrostatic pressure that varies with height.)If I exert a pressure at the top of a tube, the pressure at the bottom of the tube will not be the same. It will be larger due to hydrostatic pressure (ie. the weight of the liquid itself)