I have been studying this closely myself, and have reached some conclusions too. I had the sense that given a 26 lb weight loss, I ought to be performing better. I have a 20 mile route for weekday rides when I'm pressed for time. All season I've been doing it at 16.5 mph, on the slow side for me. It's been hard to understand.

I hit my target weight a few weeks ago, and have been reintroducing fruit. But I went to Italy for 2 weeks, got back a week ago. Was unable to restrain myself in the land of pasta, so last weekend my glycogen was fully tanked up. I felt more energy on my ride, and clocked in at 18.1 mph. That's a big difference, a full cycling category at least. I have repeated this twice, eating ~100 carbs/day instead of 20.

Similar results with tennis. More stamina, shorter and better recovery between points with carbs.

For me, LC is great for weight loss, but I pay a price in athletic performance.