Williamson says that one of the corporate heads will come down to re-close all of the lost contracts under the pretense of being the company president just in town for today. This is the exact same schtick that we see several of the salesmen use. This suggests that there's not much difference between the bosses and the rank-and-file salesmen. Maybe the salesmen have a point that it's just the leads holding them back.
Much is made of Shelly's capable sales skill in his earlier days versus the present, but nobody says aloud one of the main possibilities he's losing his touch; he's an old man now. Physical appearance plays a large part in first impressions, and people are less likely to trust a strange salesman if he's elderly and wonder why he's still doing this job.
A look at the sales board while Blake is giving his speech makes it clear that unless one of the others pulls off a miracle, Roma will certainly remain on top and win the Cadillac. It's possible Mitch and Murray arranged the contest precisely so that their one truly effective salesman would both stay and get a nice reward, while two of the three 'dead weight' employees would be fired and the last one only receive steak knives (as opposed to Roma's much more valuable prize).
If Levine back in his prime behaved as insufferably towards Mitch and Murray as he does towards Williamson in the film, the contest would also have the added bonus of allowing them to pay him back now that he's no longer their top closer and likely won't be ever again.
At the end of his rant against Williamson, Roma describes the prime advice that Williamson failed to heed as "You never open your mouth till you know what the shot is." After Roma leaves the room, Levene continues berating Williamson about his error, and ends up inadvertently giving something away that he didn't want Williamson to know—thus making the same blunder that he and Roma were chewing out Williamson for making.
