McQueen was cool but really pretty limited as an actor.
Really? And then you go on to include in your list of 40 best:
All the aforementioned actors are as "limited" as any actors who have come down the pike. However, being "limited" can be quite meaningless in the face of unrelenting charisma, charm, badassery (McQeen, Mitchum, and Eastwood in particular), and star power. In nearly every role these guys played, you always knew it was them but hardly anyone cared because of what they all brought to their roles.
Although the o/p listed character actor as one of the criteria, that is the one acting trait I would have eliminated in choosing the top 40 actors. Most of the actors listed in this thread aren't character actors.
Most of the best character actors in Hollywood history -- actors who can cover themselves in a character to the point you don't even see the real actor or actors who specialize in a particular type of character -- usually aren't all that well known by their names. Guys like Johnny Depp, Marlon Brando, James Dean, character actors who become movie stars, are rare indeed.