The Concept of Capacity Reserve

Everyone has a ceiling; a personal 100%, and a hard 5-minute round might cost you 80% of it, and pushing that pace repeatedly will quickly drives you past what's sustainable.

Get more explosive, powerful, and efficient, however, and your ceiling rises. The same rolling pace now costs less; say 70% instead of 80%, because the energy demand to sustain that pace hasn't changed, but your capacity has. Getting more powerful is itself a form of getting in better shape: game pace becomes a smaller fraction of your maximum capacity.

Your conditioning hasn't changed, but your reserve (the gap between what you're doing and what you're capable of) has. That gap determines how hard rolling feels. A bigger reserve means the same output feels easier, taxes you less, and can be repeated more times before you break down.

Note: this borrows from the idea of "anaerobic speed reserve" in track and endurance training, where it refers to the gap between an athlete's all-out sprint velocity and their race pace; where the bigger that gap, the more efficiently they can hold the slower pace.

The difference being that in running you have two poles of max sprint speed and aerobic threshold speed (the slowest speed at which you’re already flat out aerobically); two genuinely different qualities, where BJJ only has one axis (explosive ceiling), with rolling pace held roughly constant, so it's a bit simpler than speed reserve, and more like "percentage of max output" than a true dual-quality reserve.