As someone who was old enough to remember that day, and someone who has visited the museum at the Texas Book Depository and seen the actual area Oswald had set up as the sniper perch ... the best shot he had was the one he took. He was hidden in a corner with boxes of books stacked around him ... the angle he had kept him from being detected from the street. A front on shot would have meant high exposure for the sniper.
I'm also a former Marine who qualified as rifle expert at the range. Oswald qualified as a marksman the lowest catagory, the next is sharpshooter then expert.
Oswald qualified in USMC basic training as 'Sharpshooter' with a score of 216. He was two points from 'Expert'. Later, in the fleet he shoot pizza box then went Unq.
Oswald's boot camp marksmanship score places him ahead of 99% of the American shooting public.
But for Oswald to know about the route change that day, someone would have had to have told him in advance for him to have everything set up. At the least, it’s conspiracy but who else was involved even if they didn’t shoot at the President?