There were 20 4-year college guys picked in the first round of the 2015 draft. 12 of them have now reached the majors, 8 have not — including 4 who were drafted ahead of Stewart (including Dillon Tate at 1:4).
2016: 2.82 ERA the last two months.
2017: 3.41 ERA the last two months.
2018: 2.61 ERA the last two months (two starts remaining).
I don’t feel like 2018 proves anything more than the last two months of 2016 or 2017 did. You are jumping to conclusions prematurely IMO. That’s not the same as saying you’re wrong. Time will tell on that one.