You're still rendering the mesh 50 times, you're just doing it onto a texture rather than into the back buffer. It doesn't magically remove those triangles from the rendering pipeline. It would, in fact, be slower than simply drawing 50 meshes since you're now adding the overhead of the 50 sprites and uploading 50 textures every frame.
You could amortize the cost over several frames if you don't update every sprite every frame I guess. But I imagine the savings are going to be minimal at best.
You could amortize the cost over several frames if you don't update every sprite every frame I guess. But I imagine the savings are going to be minimal at best.