I'm not exactly sure but the world record holder for the Speed run% category seems to started the speed pad earlier compared to any of the other runs. If this is something that cannot be replicated, shouldn't it be considered as invalid since it gives out a huge advantage compared to others?

Hey! This doesn't seem to be the case for me, could you record an example?

Sure, here's a comparison between the top 4 speedruns I had access to. It's not very accurate but you'll notice some things.