I don't think either of your arguments are poor, but I really don't think it's that close. Chapman's added reps is a huge boost for his case not because he accumulates the advanced stats, but rather because he's able to maintain his elite defensive performance over a longer sample. Chapman has some absolutely nutty defensive numbers from earlier in his career (66 DRS, 31 OAA his first 3 years, with 2017 only being half a season). He also has much better physical tools to go along with the instincts that make both such good defenders.
Chapman speed + defense + arm strength:
Espinal speed + defense + arm strength:
I feel like if we can agree both have similar defensive "chops" (instincts, footwork, hands, etc.) then it's safe to say Chapman with his superior physical tools would be just as good a defender at 2B with the ability to play SS quite adequately. We saw him play there plenty on some of the shifts employed and he fared just fine. Espinal's arm strength really pushes down his defense once you move him from 2B to SS/3B that needs longer throws IMO. Chapman's arm would be wasted at 2B so perhaps he would suffer in the opposite fashion.