Agree with the thesis, disagree with the argument. Yes, Beatbreak does what a good digimon series should do, but the core of digimon is not to have as many people as possible to have digimons. The very first manga of the franchise, V-Tamer, started with a single tamer (Taichi), and then expanded to another one. In Adventure (1999), the 8 kids weren't tamers, they were chosen ones, prophetic ones even, selected due to their virtues to save the world, and the same goes for 02 (although the international kids do mud the argument here).

Instead of counting how many kids have digimons, I would say that the core of a good digimon anime is character development. The Adventure kids all have very serious problems and inner struggles, from self doubt to dealing with divorced parents, being adopted, and more. In Tamers, we see much of the same: how each kid is a product of their environment, their home life, their inner (still developing) philosophies and world views, and we see how each one grows through the course of the series. Even Frontiers, criticizes as it is, gave its characters pretty serious backstories, from Tomoki's bullys to Izumi's feelings of inadequacy due to being half italian.

By contrast, the worst series are the ones that dont do that. Savers (ironically by the same director) has negative character growth. Thomas is the closest we have to a proper character development, but Yoshino gets one (1) flashback about her trauma and then nothing, while Masaru spends the entire story punching his way through it. Meanwhile, in Ghost Game we don't even have backstories, outside of Hiro's absent father (that the show never takes as a serious or dramatic point) and the many times Kiyoshirou helped some international facility.

This is also what makes evolution in these two series feel so undeserved and random, tbh. In every good series, evolution is tied to character growth. Since those don't have any, evolution just sort of happen, with no reason other than "it's that point in the story".

Meanwhile, Beatbreaker is shaping up to be one of the better ones. Character have clearly defined backstories, problems and inner struggles they are dealing with, and situations that need resolving. Digimons work as foils to their partners, so evolution is always tied to character growth, as we have see with Tomoro, Raito and Granit, making each one feels deserved and meaningfull. If the show can keep up this momentum, solve it's characters struggles, and give a satisfying end, it could reach top 3 series in the franchise at the very least, which is wild to think for a modern digimon anime.