I guess the answer is that cardio alone is not optimal. But how non-optimal is it?
Around 2/3 iirc. But if we make a chart with the y axis as quality of Life and x axis as quantity of life, area under the curve is hugely dominated by quality of Life improvements of exercise because quantity gain is only about 6 years in expectation. In that regard cardio and weightlifting Grant different quality of Life improvements. Sorry for random caps my phone appears to be dumb and not smart at all.
If you want to split the difference learn to row. Uses about 80% of the muscles in the body.