There are a lot of crucial details you're sweeping under the rug in this analysis.
First, Grichuk is almost certainly in his prime or starting his decline. Age 27-32 hasn't been considered prime years since the steroid era.
Second, the most egregious part of the signing was that they bought out his arbitration years to pay him that contract. As such the optimistic dollars per WAR valuations are inflated. And perhaps more importantly than the dollar cost was the fact that we gave up a huge amount of flexibility, leverage, and risk management. If he didn't sign the extension, we could easily bring him back after this down year for a bargain in arbitration, or even non-tender him and resign him as an even cheaper free agent. Or at the most extreme cut him completely to extract value from the extra roster spot. Now we're stuck.
Finally, your outcome probabilities severely underestimate the risk associated with a player with Grichuk's batting profile. His quality of contact was good at the time, but as the Morales signing demonstrated to us directly, hard hit % doesn't guarantee a breakout. But far more important to his projections is his abysmal K-BB numbers. There are very few players who can sustain success with numbers that extreme, and he's just a handful of extra strikeouts or fewer walks away from becoming unplayable. You make it sound like Grichuk sucking is a freak outcome, but in reality his profile is one of the riskiest you can find.
This was another example of the front office bidding against themselves for a profile they liked. The reasonable AAV mitigates some of the negative value, but this was not a good signing that didn't work out. This was a questionable signing that may work out but hasn't so far.