Aerobic Base Training: Mitochondrial Density vs Lactate Shuttle

Hello! I was reading this blog post on the physiology of aerobic base training, and I had a question: does the “lactate shuttle” part of the aerobic energy pathway ever become the limiting factor of aerobic performance? In other words, is there a point in which the mitochondrial density of your slow twitch muscle fibers (in which training below your aerobic threshold improves) aren’t being fully utilized, and the bottle neck of your aerobic energy system is the speed/efficiency in which the molecules can transport lactate to the mitochondria dense slow twitch fibers (this efficiency which can be trained by training near your lactate threshold, but is also largely based on genetics)?

Thanks so much for your insight, and I hope that question makes sense. And if you think any part of my above understanding of what is happening physiologically is incorrect – please let me know!