My understanding is that Unity’s Mesh class allows up to two textures (using UV and UV2), and if you want more than that then you need to write a shader that lerps multiple textures together ? Or am I missing something?
You are missing the understanding of the interaction between UVs and textures. You can use as many textures as you want; even if you consider two textures to go with one UV set each, you still need to decide how they mix. You may need to get creative with render pass layering if you need various textures mapped in completely different ways.
So it’s all done in the shader?