FYI, there is a guy in the Starting Strength community who had pins throughout his legs as a result of falling off of a roof. His bones became so much more dense as a result of lifting heavy that he had to have surgery to have the pins removed; they were literally being pushed out of his bones. I don't think any amount of nutrition is capable of something comparable.

If you stop to consider what's going on, it makes a lot of sense. Your body is adaptive. This includes bones as well as muscles. In the same way that you need to add muscle mass in order to lift progressively heavier weight, your bones, too, need to become stronger to support lifting heavier weight. They do this by becoming denser.

Do you have any sources for those claims?

Brisk walking [every day even] doesn't qualify as a moderately active lifestyle, sorry.

If it doesn't raise your heart rate to at least 100+, it's nearly useless as an exercise. Sure, you'll burn slightly more calories than sitting at a desk, but the benefits are nowhere near actual exercise.

> more and better quality sleep, better friendships, etc.

Sleep quality generally improves with exercise, as long as you're still getting 8 hours. Better friendships are completely orthogonal to exercise/weightlifting.

Isn't such perspective limited?

My parents are 67 and 65 years old; I would say say that daily brisk walking is possibly much more suitable for them (their body) in comparison to weightlifting -- irrespective of your personal definition of "exercise". And I'm damn sure their heart rate easily exceeds 100+ if that's the main variable to control.

Brisk walking for an hour daily is absolutely considered moderate exercise. High quality relationships can reduce stress which is related to sleeping.