I’m going to give away a huge hollywood secret. the secret sauce for removing banding for web is to create a digital intermediate by exporting down to a lossless 8 bit codec like animation or quicktime png. this then forces AE to dither all 32bpc composites into 8 bit. you will then force the dither quality out before any actual compression takes place. the next step is to re-import that new 8 bit lossless back into AE with effect neatvideo. important! (AE working space needs to be 8 bpc in this step) then use its luma, chroma sliders to completely remove the banding. finally, export as h.264 for web. just don’t tell anyone this trick!
and yea, noise increases file size by 20-30% btw. that’s why really small h.264 sizes are made from denoising before compressing.