You essentially spelled out the reason why Rad Onc is more competitive. Absolutely the board scores, match rates, and percentage of applicants are about the same, however there are several critical differences which make Rad Onc more competitive.
The first comes in the last point you mentioned…publications. The average this past year published by the NRMP for Rad Onc was 8.0…this was in comparison to Rads 3.5 Also a critical difference is the number of applicants with a PhD, Rad Onc 20%, Rads 5%. Essentially Rad Oncers have the same benchmark numbers, however we dwarf Rads in terms of research. So if you were to take the average Rads candidate with three publications/presentations its pretty unlikely they would match in Rad Onc, let alone match well. On the flip side if you take the average Rad Onc candidate they would very likely match extremely well in Rads. Publications are a great reflection of true competitiveness of a specialty; the top two being Categorical Plastics and Rad Onc.
Anyone can score a 240 on step 1 and get AOA, however very few can do that while at the same time juggling 8 research projects. Having a smaller total percentage matched does not mean that a specialty is necessarily more competitive, just because more poorly qualified people apply for that specialty does not mean its more difficult, its just more rejection emails the programs have to send.