I think the difference between Challengers and ATP events is much smaller than you're acknowledging, and the fact that players like Dodig, Marchenko, Stakhovsky and Zeballos had a good run in at least one of those events this year illustrates that. If anything, the fact that the points you can win in Challengers have been lowered this year is a bad thing.
I don´t think so. For me it is a huge difference to beat at least one Top 10 to Top 30 player and several from the Top 50 to win a World Tournament or to beat one player out of the Top 100 and the rest from 100-300. This is not a "small" difference. My proposal: just give Challenger tournaments more prize money but less points.
And for me it is "luck" if a good challenger player reaches a final or semi final of a World Tour tournament. A good draw and luck and there you are. It is logical is that these players are not able to repeat such a success immediately. For me, this is a "one-hit-wonder" which is nothing unusual.
Just look at Zeballos: besides the "lucky strike" in St.Petersburg, there was nothing at all on the tour. The ranking points table is a joke.