Seems like it's not that simple. The CHOICE study[0] suggest that some brands do have some good "models" of sunscreen, but some are bad. It's also possible that there's a process issue at the manufacturers, and the quality of different lots can vary:
> Ultra Violette announced it was removing the Lean Screen product from shelves. Across eight different tests, the sunscreen returned SPF data of 4, 10, 21, 26, 33, 60, 61, and 64.
> Ultra Violette announced it was removing the Lean Screen product from shelves. Across eight different tests, the sunscreen returned SPF data of 4, 10, 21, 26, 33, 60, 61, and 64.
[0] https://www.choice.com.au/health-and-body/beauty-and-persona...