Improved mitochondria function means improved energy conversion (in other words greater ATP with less calories)...that seems pretty useful all by itself.

Improving ATP efficiency is huge... i agree with you it may not mean stronger bones and more elastic skin...but we do know aging (less elastic skin and weaker bones) is related to the bodies breakdown in ATP supply/demand/conversion.

I just don’t think you can gloss over mitochondria inprovement as no benefit...it’s literally an improvement in energy (more energy with less calories), it’s a benefit unto itself.