Within some mental model, isolated protein powder is healthy because we generally treat high protein consumption as low-risk for most people and recognize that protein isolates can be very effective for professional and amateur athletes to consume a lot of while building muscle.
In no way does that imply that these protein isolates are "extremely healthy" for the general public or even for anyone in the long term. There's just not any data to say that specifically (it's too niche to perform those kinds of studies), and far too little reason to make that assumption with confidence.
(And it's almost certainly a terrible idea for most people to eat 4-5 chicken breasts per day -- or a comparable amount of protein isolate powder. Please remember that most people are not living a gym bro lifestyle and shouldn't be following gym bro nutritional advice in the first place.)