I don't agree with giving Tellez more at bats, but agree with the rest. Sign Edwin if you think there's a chance to contend in 2020. He's still a good hitter. However, the Jays have a lot of holes, and spending $10-15m (or whatever it would take) to sign a 37 year old DH when you need at least 3 SPs, a CF, a pen, etc, is kind of pointless. If you could fill all of those holes AND sign Edwin, then that's a different story, but even then as you said getting a younger talent on a longer deal (not necessarily Ozuna/Cast) would be more advantageous.
A player like Edwin would have worked for the 2016 team that had a chance to contend and needed short term wins wherever they were available. I don't see it as a great fit for the 2020 team. Plus I'd prefer keeping DH open to rotate players around, especially since we don't know what shape Vlad will be in come March.