I’m guessing you misunderstood the question sorry, the point was that I wanted to end up with a decent H264 file… but doing it in two stages seemed to be quicker than doing it directly in AME. Which seemed strange to me. So I wondered if AME was well known to be slower to render from after effects, or if AME maybe struggled to output certain AE effects or something.
Otherwise in future I might keep doing it in two stages, at least for bigger projects, as it seems to be 10-20% faster to do it as a two stage process, instead of a single export to AME.