Fixing metabolic slowdown isn't going to end obesity or reduce the need for exercise, but it will level the playing field.
It's still going to require effort, for many people, to maintain a healthy weight and exercise enough. But it's hard enough to do that as it is; if you can turn off a defect that causes the body to pile on unneeded pounds of fat (that interfere with health, mood, and the ability to exercise) with age, then you should.
How is metabolic slowdown a defect? I don't see middle-aged people dropping dead around me, so clearly all that has happened is that their bodies are now more efficient. Great news!
And piling on fat making it harder to exercise? Sure, on the face of it that's true, but usually the one happens because theres a dire lack of the other.
It's not basal metabolic rate that makes people fat. It's either unhealthy cracings or low energy (and yes, I know that this sense of "energy" is psychological to some degree) levels.
It's not low BMR alone that's the problem and, of course, if you have a high BMR but cravings/appetite issues or lethargy, you're still likely to gain weight.
It's still going to require effort, for many people, to maintain a healthy weight and exercise enough. But it's hard enough to do that as it is; if you can turn off a defect that causes the body to pile on unneeded pounds of fat (that interfere with health, mood, and the ability to exercise) with age, then you should.