I went into this dynasty knowing that Legendary mode would be nearly impossible. Most people have a hard time winning games with decent teams on Heisman and default sliders. So, having a terrible team and sliders maxed out against me... well, I knew the challenge ahead of me.
Having said that, I started fresh, started from scratch, pretended I knew nothing about NCAA, and just did my damndest to win ballgames. I had that "anything goes" mentality - and, trust me, the CPU is so good at this level that it demands this mentality if you want to stay within 50 points. If the competitive evolution of the game took me in a certain direction - regardless of what it is - then fine. The direction happened to be scrambling QBs.
In short, scrambling with a fast QB is the best and most effective way to score points against Legendary mode, as far as I can tell. Now that this has been proven and has gotten redundant, even though I didn't win a ton of games with it, a QB speed cap has become necessary.