You should not be skeptical. Wariner and Merritt are two of the best to come around, ever. Wariner has been at the highest level for a decade. 10 years of sub 46 runs, no serious injuries. 8 years sub 45. Some folks get older and cant run fast anymore. Maybe he will again. Only he knows.
Merritt just a two years off? He came back and ran 44.35 last year. He has been talented since the junior levels. He will do it again.
Don't include the young 400 runners yet. Although talented and young they have not broken through but they will. Most of these guys are either 1 year removed from college or still in college. Try running a collegiate season of indoor, outdoor, and rounds in a world championship and clock a huge time. Its damn hard. Wariner did it because he was super talented.
The hurdlers you speak of are all getting older. Clement, Jackson, Sanchez and Taylor are not young but they still have it.
The young hurdlers Dutch, Anderson, Wyatt, Van Zyl, Gordon, Fredericks will get there but you cant do it over night, or over one season. It takes time.