Put another way, the type of person who is naturally “boring” and not very reactive probably won’t get themselves tangled with the kind of person that needs to be “grey rocked”. If you are always a gray rock, then you are not an easy target for a manipulator.
If you find yourself in the blast radius of an abusive narcissistic person for example, grayrocking is totally a decent way to deal with them, while keeping your calm. But using it towards everybody whom you're not 100% on board with is probably a bit overkill.
It is unhealthy simply because it's a rebranded form of passive aggression. The real problem is not yet having figured out why someone like that can get under your skin in the first place.
The exact same situations that can bubble up unhealthy amounts of negative emotion in younger people don't do that in older people. Older people have already been there and done that. They fully understand the behavior and instead of anger or retaliation they usually feel pity or nothing at all. Which mind do you think is healthier?
In other words, there's no escaping life's lessons. Your best bet is to minimize the unavoidable consequences and stay out of trouble. For sure, a big part of that is cutting out bullshit like Esquire. This "grey rocking" stuff is just woo woo nonsense that was meant to prime you for ads that already happened back in 2021.