At what point did I say Syndergaard "wasn't worth trading for"? You guys continue to look at these things in a vaccuum and act like the only players involved were the two of them.
AA was making a win-now push and had just traded for Mark Buerhle, Jose Reyes, Josh Johnson, and John Buck. Dickey was coming off a Cy Young season where he struck out 25% of the hitters he faced while walking less than 6%. They also got Josh Thole, who was Dickey's personal Catcher. Syndergaard didn't even make the top half of FanGraphs' Top 100 prospects lists at that time, and couldn't throw a breaking ball for strikes. He was #64 - behind future "Aces" Justin Nicolino, Drew Hutchison, Daniel Norris (all 3 ranked ahead of him in Toronto's system), Taylor Jungmann, Tyrell Jenkins, Daniel Corcino, Trevor May, A. J. Cole, Drew Pomeranz, Manny Banuelos, Mike Montgomery, Randall Delgado, Zach Lee, Martin Perez, Matt Harvey, Arodys Vizcaino, Jarrod Parker, Danny Hultzen, Jacob Turner, Zack Wheeler, Archie Bradley, Tyler Skaggs, Jameson Taillon, Trevor Bauer, Gerritt Cole, Dylan Bundy, Julio Teheran, Shelby Miller, and Matt Moore. He was Folty when the Braves traded for him. Apparently AA wasn't the only person who missed when projecting him, and that probably has a lot to do with why he's been gun-shy about trading from this group of arms.
There's no doubt the Jays (and AA) "lost" the deal, but the teams both had completely different motivations - AA was making a push at the time and needed a frontline SP (which Dickey was at that point), and he got one with two years left on a manageable contract. The Mutts had no farm system and were looking to build one. They gave up a quality major league asset for a RAW young arm and pretty well thought of Catcher prospect (d'Arnaud).
Syndergaard was the equivalent of an Anderson/Touki/Gohara type at that point. The fact that he worked out is what bit the Jays in the *ss - just like the fact that Folty looks like he's going to work out makes the Astros front office at the time he was traded look "dumb". Those things happen when you make win-now trades. Chances are, if AA gives up Riley and Anderson/Touki/Gohara for two years of Realmuto he'll regret that too because at least one of them will reach their ceiling. The Mutts got two Top 100 prospects (neither in the Top 30) - #64 and #37 - for Dickey and a backup Catcher who could handle the knuckler (which is usually pretty tough to find as well).