Of the non-runners I've talked to who are interested in normal sports like football and basketball, I'd say close to 1/3 know who Justin Gatlin is, but none know who Wayde van Niekerk is.
The 200m and 400m are the weakest events. In fact, I'd say that the 200m is almost pointless. If 400m runners could easily move up and dominate the 800m, they would, because the 800m is far more prestigous. A 400m/800m double is an incredible achievement, meaning you are a master of both sprinting and middle-distance, and that's why Juantoreno is still a legend after 40 years. If VN could easily move up to 800m and crush Rudisha, he would, because in doing so he'd become the greatest and richest athlete ever to have stepped on a track. He wont, and Rudisha will remain many times more famous than him.
Actually, if he beats Usain Bolt's 200m record, which he is supposedly trying to do, he will be 100x more famous and rich than Rudisha.