I didn’t see deferral percentages for this year yet, but in a recent previous class (https://www.thecrimson.com/article/2017/12/13/early-admissions-2022 ), Harvard deferred 74%, accepted 15%, and rejected only 9%. Being deferred does not mean you are a borderline applicant who has a decent chance of admission in RD. Instead it only suggests you are not in the bottom ~9% of SCEA applicants. The overall RD acceptance rate was only ~3% that year, and deferred applicants typically have a much lower acceptance rate than the overall RD rate. In short, unless something changes between the SCEA and RD round that makes the application far stronger, a deferred applicant should expect to be rejected in RD.