Without analysis of the counter-factual, the list seems impressive. But had Howland died there is a high probability that there still would have been a 32nd, 41st, and 43rd US president; prominent 19th century poets; Alaskan governors; pediatricians and Hollywood leading men. And listing both Bush's seems gratuitous - why not list all the Baldwin brothers? Probably the only two individuals on the list whose impact on…
There's a famous Twilight Zone episode about a time-traveling assassin who kills baby Adolf Hitler. The episode concludes that nothing really changes, as another child growing up in that environment becomes just as bad as an adult. I'm not sure if I believe it, but it's an interesting argument. There almost certainly would have been people in most of those positions, though perhaps not with the same quirks.
In other words, it is likely that Dole [had he won the Republican nomination] would have defeated Dukakis as readily as Bush did in 1988, or that Carry Grant could have starred in The African Queen.
On the other hand, the specifics of Smith's personality and circumstances are hard to separate from the movement he spawned.