Rebuilding in the shadows and rebuilding are two different things. Or at least two different strategies. In no way were the Jays rebuilding in 2017 and 2018. In the background, sure, they made sure the farm system was being taken care of, but in the forefront they held on to players they should have moved and let big league assets depreciate in value before trading them.
My example of rebuilding in 2018 would have been trading Donaldson to the Cardinals in the winter and then starting Solarte at third. In hindsight Solarte sucked, but you could have at least projected a 1-2 WAR out of him, while maximizing the return on JD. That's the type of off season the Jays should have had here. They are obviously salivating to trade Stroman, Sanchez, Giles, etc, but wanted their values to increase, but what stopped them from signing good vets instead of spoon feeding playing time to Hernandez, Drury, McKinney, Brito, Hanson, etc? Why sign Galvis then, should have just went with Gurriel and Urena and lived with the consequences.
The Jays partially rebuilt in 2017 and 2018 (and even 2016 when they were adding to a playoff team), but no way were they really rebuilding. There was more value wasted in those three seasons than anything else. This team took a huge hit by waiting to trade certain players.