How about The Untouchables? The movie went completely off the rails at the end where “Frank Nitti” (played by Ed from Northern Exposure) is killed by Elliot Ness in a shootout. Shame on you, David Mamet, for that screenplay.
Nitti’s portrayal in The Road to Perdition, written by Max Allan Collins and played by Stanley Tucci, was dead on accurate.
The Untouchables was a Romanticized piece of historical fiction. No one claimed otherwise.