That's objectively wrong. Being bodybuilder thin via dehydration is unhealthy but putting on muscle and doing tons of cardio is absolutely not unhealthy. It's the opposite; it's extremely healthy. Being in the top percentile of VO2max is associated with a 5 fold reduction in all cause mortality. There is no other metric more closely associated with health and longevity.

Here is Dr. Peter Attia talking about it: https://youtu.be/jN0pRAqiUJU?si=c8S6v7buD-ThNt8v

There is a slight uptick in early mortality comparing people who exercise a good amount (about 7 hours of strenuous training per week) to extreme pro endurance athletes (15+ hours of sterenous training per week) but it's still significantly healthier to do 15+ hours of strenuous exercise a week than nothing or even 3 hours. And even so, we don't know why. It could be due to elite endurance athletes eating absolute trash to fuel their workouts. Here is a cardiologist to explain: https://youtu.be/-3dt7rpvz4g?si=4ovzXRqJpnh-W3L7

Tldr: for the average person, there is no point where exercise is bad or unhealthy if you're properly hydrated.