Ablation leaves lesions that become fibrotic as they heal. Fibrotic tissue is inelastic and more resistant to changes in geometry. So, yes, technically, there is a reduction in output after ablation
from the output of the pre-AF healthy heart. During AF, the heart's capacity in obviously compromised, as should be intuitively clear. However, I think the net is going to be considerably higher for a heart in NSR and whose valves, all four, are in good health.
Subsequent ablations should increase the amount or extent of fibrosis is one assumes that the subsequent ablations are necessarily going to have to zap healthy tissue over which SA node or AV-re-entrant signals are still getting through and causing ectopic beats.
VO2 Max is a function of the circulatory system working in concert with mitochondria in skeletal muscle to convert glucose or ketones into energy using the available/free oxygen. You have as much to gain by physical training to improve VO2 as you do in returning your heart to NSR.
Not just VO2, but lung capacity, bone density, the degree of heart disease as one ages, and not least, muscle mass and tone in the skeletal masses meant to keep you erect and functional...and out of a wheel chair. Don't forget a healthy vestibular system. Falls from vestibular disorders are more lethal as we get past 75 or so, with variance.