He can beat Mo Farah at London and maybe Shura Kitata again. Mo and Shura could likely be some of his best competition for Tokyo gold in 2020. He also knows the course obviously and has success there. If he ran Boston or NYC in 2019, yes they're more strategic but he'd probably run slower, without pacers as those races aren't only about fast times, unlikely but a small chance he could lose, depending on the field. At this point if he keeps winning and runs fast he can mentally own his competition too, make them think they can't beat him. Tiger Wood's them. More likely they'll do something not too smart if they're not sure they can beat you. If he wins NYC in 2:06 for example next fall, a lot of guys are going to think,...I can run 2:06, and if they ever run together in a race later and it matters they might think they can beat him. Keep the legend going.
If he owns his races until Tokyo, he'll own his competition. Save NYC and Boston until after Tokyo Kip-epo-ge!