I think they were saying that many of the effects cancel out over multiple lengths, as you're slowed down one way and sped up the other. It's not a perfect canc

I think they were saying that many of the effects cancel out over multiple lengths, as you're slowed down one way and sped up the other. It's not a perfect cancellation but it does diminish the problem. However the 50m is just one way, so you get the entire effect with nothing cancelling it out at all. There's also then a much bigger difference between lane 1 and 8. If everyone did two lengths, then lanes 1 and 8 would have been penalised a bit (faster one way, slower the other) but they'd have done the same as each other. Lanes 4&5 would have been a bit better. Now picture just one length. Lane 1 never has to swim against the current, while lane 8 has to fight it all the way.