When you create the WVP matrix on the CPU you'll only have to go through this process once for every mesh. However, when doing this in a shader it'll have to be done for every vertex.
Aha, that would be it. Thanks. My meshes only have a few dozen vertices, so shader matrix multiplication still might be faster. Probably faster.
This is a webgl app, so I'd have to test how it works out on low-powered devices with integrated graphics.