As far as I know, the vertex shader is only more performant because (in most cases) it results in less times the material is calculated.
There’s over 2 million pixels in a 1920x1080 resolution. If you’re material is displaying on half the screen, you can imagine how many times it’s being calculated. So, if your mesh has 5k verts, and it only calculates per vertex, you can see the gain.
So, even if your mesh had enough verts for the vertex shader to reach the same fidelity as the pixel shader, there wouldn’t be any performance gain. In fact, I imagine it would be worse because of the screen-space issue @Frenetic mentioned. If your mesh takes less screen space, it’ll cost less on the pixel shader, but the vertex shader will remain the same (outside of LODs). Throw nanite’s 3x and it gets even worse.
TL;DR: The vertex shader is not inherently more performant than the pixel shader. Whether you should use it comes down to the fidelity you need in a material. The vertex shader generally isn’t useful for displaying textures, it’s more useful for displaying static or gradient values (eg: flat/gradient colors, like you see in stylized assets, like leaves on a tree).
Whether you should use the vertex shader should generally feel obvious. If it doesn’t, you probably should stick with the pixel shader.
But, I’d also add the vertex shader can be used for all parts of a material individually (eg: metallic and roughness could be on the vertex shader, but color could be pixel). Do with that what you will.
And, 4 textures really isn’t an issue. I’ve seen much, much worse. 