Gal Gadot would have been closer in size to Reacher than Cruise. True story.
Seriously, liberties are taken from time to time with characters, especially with ones played by Cruise. For example, just look at Minority Report: In the short story John Anderton is a 50-year-old balding, out-of-shape police officer who created Precrime, while in the movie Anderton is in his late 30s, handsome, drug addict, athletic, with a full head of hair who joined Precrime after his son's kidnapping.
I still maintain that with Reacher his size is part of his character. It's emphasized and focused on in every novel. Those who have read the material understand.
Casting Cruise as Reacher would be like casting someone like Peter Dinklage to be Andre the Giant. In reality, any actor hired to play Andre should be a giant actor and not a tiny one. Cruise as Reacher is as striking of a difference as those two would be. Because Reacher is fictitious people are quick to dismiss his characteristics. Much quicker than if it dealt with a real man who was 6'5 250 lbs.