Strictly speaking my comment was aimed at comparing 28g loads V 24g, I shoot almost exclusively English 8's (yes there are times when I have had to change to 7.5's when for instance trying to change brands etc,) but given the choice it's 8's. Therefore whenever I have conducted these types of tests ( I have also done it with 21g) I have made sure I sourced 24g loads in English 8's to keep the shot count as high as possible, I found that as good as 24g loads are, they are not a match for a 28g load, like for like. The question of fatigue is a very valid one particularly when doing hundreds of rounds per day but in my opinion most shooters myself included, can weather the storm of a 100 birder easily enough.
This is a very difficult subject to conclusively argue or decide one way or the other because we have to understand that human error itself can mask a good deal of "reality". If we were shooting going away Trap type targets at range or perhaps even bio's (which are supposed to be harder to break), then it may well be provable that in fact 7.5's (despite their lower shot count) would trump 8's simply because individual pellets of the latter may lack the power to cause a break on these edge on clays, only lab condition testing can prove one way or the other.
In ESP I found that smaller loads lacked the fringe benefit of the 28g loads, we all like to think we centre things but the truth is we don't as the dozens of poor and half hearted breaks we all get per round will prove.
In answer to your question if I had to put money on the subject then YES, I would say if you gave a thousand shooters 24g loads of number 8 shot V another thousand being given 24g 7.5's and monitored their scores properly, the smaller shot size would "luck" into a few extra breaks and win overall, at English sporting that is.