In fact, I specifically addressed the case of an "A player" having a dip in productivity, and essentially said there is nothing wrong with that. They manage their time and their output accordingly to strike an appropriate work/life balance to take care of what needs to be done outside of work, and also manage against burnout when they've been pushing too hard for too long. And the fact that they manage this effectively on their own and can get back into things is part of what distinguishes an "A player" from a "B/C player."
The A/B/C boxing is just a shorthand for categorizing overall performance of people on a team. But if you think it is an inappropriate way to classify individuals, I'd love to learn how you approach it, and how much management experience you have with that approach.