Sorry, when I read "lineup core" - I though offense, not defense. To be honest, despite his WAR totals, I never considered Kevin Pillar as part of the Jays "core" in 2015 or 2016.
Their offense was 10th of 15 in the AL last year. A full season of Trout and Upton will certainly help, as will whatever Ohtani provides, but I just don't see them as a good offensive team. The rotation could be good, if healthy - but that's been a massive issue the past couple of years. They were 5 games out of the 2nd WC spot last year and 11 games out of the 1st WC spot. They don't even have any young players in their lineup who are expected to make significant improvement (unless you believe in CJ Cron - which you shouldn't). They are going to have to continue to add payroll to make this a "good" team I'm afraid unless they incredible lucky with SP'ing health. That blueprint rarely works.