I'll take a crack at answering my own question as it's been some time.
So after doing some googling I've found a few articles that claim Butch Cassidy and The Sundance Kid is symbolic of idealized manliness. If this is true then I would conjecture that LeFors is merely the law man the biggest toughest guy in the room that they cannot overcome but are able to elude putting them on par with Lefors as far as manliness goes.
However when watching the movie myself I tend to take the main duos actions more so as childish and whimsy. Constantly jesting and playing tricks even in serious moments. To that effect I would venture that Lefors is more so a stern father figure or figure of maturity that they are always eluding. This is primarily due to the fact that Butch mentions if they get caught they'd go to jail instead of hanged which given the time/decade and the lot of crimes they've committed, Sundance having even killed people, would seem odd. Instead it is more of a disciplinary/corrective action
In the end, still being the playful bunch unwilling to hold down/given up on a job, they are more concerned of Lefors, maturing, and embrace the ideal childish fantasy of guns blazing youthful joy is more fun than facing the scrutiny of labor/maturity.
But then again this is just my own conjecture/analysis.
But then again this is based on a true story and maybe the author just wanted Lefors to be Lefors and just threw him in.