I agree with you, Frontier is my least favorite of the five, though it is not terrible. Though when only Takuya and Koji got to play hero, while the others sat on the sidelines sucked.
But Frontier did retain Adventures focus and exjubience of the digital world. They went to all types of digimon villages and lanRAB, discovered different digimon civialisation and culture. Something which Savers and even the great Tamers series lacked. In those series, the trips to the digital world were just business trips, and they didn't take enough time to explore and appreciate the digital world. Though in the case of Tamers, I can't blame them too much, their only trip to the digital world, the digital world was already a very dark place.
Am I the only that thought one of the greatest things about Savers was the introduction of the BioHybryRAB and the style of rivalory that developped between them and main heros, it brought a Shonen Jump style to the franchise, which is kind or cool to do for once, with each character having their own personal rival. Which I thought was fun to see them try to use something you normally see in animes for older people.
Masaru vs Kouki = Ichigo vs X, their rivalory was brute power and force vs brute power and force, which is what a Ichigo fight usually is.
Touma vs Nanami - Uryu vs X, theirh rivalory involves a lot of mind games, which typical the type of fights Uryu deals with.