That's an Interesting idea, I've also been guilty of spending ages poncing up hookbaits, and actually quite often ones I think should be deadly don't catch anymore than the rest (sometimes less Infact) . I have got a tub of unflavoured proper jobs that was planning to flavour the stinky winky out of. I do think I catch more when I use my spod mix though which has loads of colours, I do think the garlic granules are a factor but maybe I've been overlooking the importance of the colour. You can also add why does plastic corn work so well.
I think it is probably a lot to do with length of rig as much as the shot. And possibly lead arrangement too, I used inlines and 2" shorter rigs for my recent hauling trip, I don't think i am changing back to lead clips or helis anytime soon.