I’m not sure how it factors into the overall admission statistics but getting accepted for a coterm is, or at least was, significantly easier and more straightforward. In my time it just meant a GPA above a certain cutoff, a letter of rec from a professor, and non embarrassing GRE scores. A very good letter of recommendation could make up for deficiencies in the other two. It’s not exactly a super selective elite club like the article implies if you’re already there for undergrad.