Roasting transforms green coffee into the aromatic material used for brewing. Moisture is lost, the bean changes physically and many reactions contribute to the flavors associated with roasted coffee. A darker appearance is only one observation within that process.
The source discusses temperature, time, changing density and the development of roasted aromas. Those measurements need context: the machine, batch size and probe position affect what a recorded temperature means. A published example is not a ready-made profile for every roaster or coffee.
For a practical comparison, keep the green lot and batch size consistent, record key changes and compare the roasted coffee using the same brewing approach. Allow an appropriate, consistent interval after roasting before comparing batches. Avoid treating roast level as a precise caffeine calculation or assuming that a single visual shade proves a balanced result. The useful outcome is a controllable roast that develops the qualities you want and can be reproduced on the equipment being used.
The conversation
A good question can make a better brew.