Road and trail running are just different sports and require such a high level of specialization at the very top that crossover is far from trivial. Kilian is still a better road or track runner than 99.999%, but he is very far from being world class in those disciplines. Flat running requires a more refined stride, better foot speed, slightly different muscles compared to going up and down steep trails. Top level track/road runners do not tend to do trail races during their peak years (there is much less money in trail/ultra than track/road), but ones who are just below then do not automatically win trail races.