Randal Grichuk was also part of the deal, IIRC correctly.
I also thought they should have traded JD in 2017, but I think ownership didn't want that. The Blue Jays wanted to be a big boy, and they still thought they had the roster to get some wins in 2018. Hindsight is 20/20, like you said, but I can understand why he wasn't traded in 2017.
If JD was having an MVP type season in 2018, instead of the injury mess that was his season, I will bet we'd have 2-3 more decent players on the roster, or minors, now via a trade. Or nothing. Prospects are always a gamble. We may have something with Merryweather. Whos's to say we would have been better off.