I think it's much more subtle...and insidious.
This movie is a fairly adept psychological drama (at least at the beginning), which would make it more akin to the original "The Hustler."
What's the key lesson Felson tries to get Vincent to learn?
That winning isn't in the stick...it's in the head.
I think Felson uses Vincent purely as a pigeon, to check out the potential competition before making a comeback WITHOUT arousing anyone's suspicion.
Frontmen are considered scum (don't forget what a lowlife George C. Scott was in "The Hustler").
So no one would suspect Eddie would ever make any kind of comeback.
But if anyone did, then they might come 'round tryin to play a psych job on him, because Eddie does house some self-doubt--which is his only weakness--about his remaining ability.
I think Eddie figures that Vincent is too much of a flake to ever really figure it it out. While everyone focuses on Vincent, Eddie can catalog the potential opponents.
I think Eddie lets himself get hustled as a complete ruse. He's too sharp to get taken by anybody. But it makes for the PERFECT excuse to ditch Eddie and the girl WITHOUT raising their suspicions about his motives. They just see him as some disgraced, washed-up old fool, and that is EXACTLY what Eddie wants them to think.
As far as Vincent himself as a threat...Eddie has him psyched out from the beginning.
But I think the interesting part is...that Vincent DOES learn the importance of the mental game, once Eddie ditches him and his girlfriend, and they have to hustle without a backer on the road.
The jibe about ditching the game is the best psych job to lay on Eddie, to try to drive a wedge into Eddie's only beloved patriot, that bit of self-doubt.
This flick reminds me a LOT of "The Grifters," as far as the tension of the 3-way dynamic between the characters.