If I did an animation say of a building in 3d in After Effects and if I did a flat version in normal 2D, would it make a difference to the final rendered file size? As in would the 2D version play quicker in the final render (say as a .mov file) than the 3D one?
File size and data rate are driven by the frame size, frame rate, detail in the luminance channel, bit depth, and compression used. It doesn't matter if you use Premiere Pro, After Effects, Davinci, or a 3D app like Blender or Cinema 4D. A five-minute 4K, H.264 MP4 will be the same file size within a few bytes and have the same data rate no matter what app you use. The only difference will be the render times. 3D projects, no matter what app is used, always take longer to render than 2D.