I am an organizational apologist and extremely biased at all times. Here are three good things about the Grichuk contract.
1. It is a good educational event for how prudent teams approach deals.
2. It shows good process by the Blue Jays.
3. It was about more than Randal Grichuk and in hindsight has paid off.
By #1, I mean to say that how Grichuk is now performing kind of shows the likely thinking of the Blue Jays at the time he was extended. Most teams would not think of these things as a simple matter of comparing the player's projection vs the cost. Rather, they think about these things via a range of outcomes. If the player really underperforms and only plays to say their 10th percentile, what does that look like? If they figure some stuff out and take off, hitting the 90th percentile of their projected outcomes, what does that look like? I think the Blue Jays obviously thought Randal Grichuk was capable of more, perhaps they thought he projected better than this or hoped he would play much better... but they probably had a sober thought that even if he were to underperform and really flatline, it would not look that bad. They would have based this on the size of his MLB sample pre-extension, his age, his ability to hit for an okay average with power even when he sucked, his ability to play decent defense. And that bottom of the barrel outcome is not playing out and it's really not that horrible. $10M each for the next two seasons for a bench quality player. The deal did not work out but it's not a sunk cost entirely and it's not the end of the world.
Contrast this to the bottom of the barrel outcomes on things like the Chris Davis extension, or some of the mid-range contracts given out historically to starting pitchers (which always carry a downside risk of literally zero production) like Jordan Zimmerman, Homer Bailey. It's possible in baseball to spend $50M+ on player talent and get zero return.
I guess #2 is already explained within the above.
And #3 is obvious too. It helps to attract guys like Ryu and Springer, and some of the lesser FA pieces, if your team is not literally all children. As Toronto planned on cycling up their payroll they had to start somewhere. An extension for a veteran currently in the organization was a reasonable place to start. Perhaps a good signal to other players in the league that the team was committed to building around the kids coming up, committed to some level of monetary spending, etc.