While I generally agree... I think his price point and initial asking price from the Jays would be justified if his performance from June was maintained. This is a rental, and recent performances that show cracks in someones game is important when assessing if the price you pay. We're not talking about 2, 3, 4 year projections here. We are talking about every start from Happ having an impact on the pennant race... so ya, 4 games where Happ showed holes in his game does matter as it erodes the confidence in the buyer that they are getting the player from June and not July.
Do you think we could of gotten the same package for Oh at the end of June? I doubt it. His bounce back in July helped display that he can still (somewhat) lock it down. It's the same reason why the Jays aren't going to sell JD for a bag of balls. Recent performance (yes, and health) for rentals plays a factor in their value.
Again, not saying this is the sole or main reason his price dropped, but a contributing factor.