a) how much of the text describes the solutioning, vs

b) text that describes the actual problem and real world cases where this was an issue (One anecdote from the author??)

As a lifelong drummer, programmer, and music producer -- following a drummer across varying tempo isn't a real problem. Any good drummer who is being relied upon to conduct the tempo will be well-trained enough to hold the tempo. Any great drummer who uses polyrhythms will keep accurate tempo regardless of the subdivisions of the beat -- otherwise the subdivisions would not land in place or sound correct. For songs that have intentional tempo variance, solutions already exist.

An app for a virtual band to follow a drummer who can't hold tempo... is a toy for amateur drummers who want to be the lead. Lead drummers are rare (Don Henley, Phil Collins, Bruno Mars, Anderson Paak) but they all know how to nail a tempo. And any good drummer plays with syncopation and time signatures far beyond what this toy tempo estimating app can deduce.

DJ/production software (Serato, Ableton) has industry-leading tempo estimation which still only reaches 1/10th of a bpm, which is ~3-10x fatter [0] than what the human ear and good drummers can hold time to [1]. There is no way that this app beats Serato, Ableton, and gets anywhere near to 6ms of human accuracy (transients etc make this hard... I have worked on BPM software).

[0] 0.1 bpm at 120 bpm = 50ms

[1] Typically ~6-10ms, see e.g. https://www.researchgate.net/publication/309706298_Effect_of...