I thought during the export, only the the things getting processed at that moment matters. Like when dealing with the footage section, only the overlay, the color adjustment and the footage itself should be processed. Those intro, fades, overlay at first were already in "past tense" and should not affect what comes after. At least in other editors it was the case. The export speed was affected by how many things it has to process at that "instance", no lingering effect from the frames long before.