I've related part of this before but here goes. My grandson talked me out a BSA B50MX I had sitting around since the 70s. Although probably originally sold mostly to dirt bike riders, it was an MX bike meant for race. On his second official heat ever, he was the youngest rider on the oldest bike and he won his heat (6 riders). The stock front forks worked properly (I rebuild them), the original rear shocks were on the bike, and it was running the original engine and tires that sat from around 1974 (yes, I know the tires part is crazy but to teach him he had to pay for everything but the bike itself).
So, like many things in racing, it's more about ball size than the equipment! Look at the senior TT. Most of the bikes can due 200mph, but most do not win!