You have to consider the fact that Taehyung is a baritone who never gets to sing like one and Jungkook is a tenor, and BTS's songs are written in a tenor range that is comfortable for Jungkook, Jimin, and Jin to sing in but a challenging range for Taehyung to keep up with. The difference between Taehyung and Jungkook isn't that significant though. Jungkook has the BEST pitch and agility (ad-libs, runs); however, Taehyung has slightly better technique and relaxation in his OWN range (the range that he's comfortable with-best support (in terms of consistency and supported range) and placement). Nowadays, BTS's songs are written in a higher range, so it's going to be much more difficult for Taehyung to keep up with. However, you said correctly that Taehyung has the "best range", but it doesn't indicate vocal skill, it indicates vocal potential, which he has a lot of.