Batutta
Major Contributor
That is simply not true, whatever codec you use in order to re-encode you need to decode it first, decoding of inter-frame H.264 will not be significantly different than decoding ProRes as long as the the video is rendered sequentially. The slowness comes only when you move the play head to a particular place, then the NLE needs to calculate the current frame if it is not an I-frame.
If you are finishing in the same ProRes format you shot in, on the shots that have no effects applied, there will be no re-encoding, just copying of bits. H.264 will always have to re-encode. So there can be a lot of time saved.