Every club has a muzzle energy limit, its just most of them go about testing the wrong way lol
Chrono's never used to have energy conversions on them
and nobody had heard of fps to energy conversions back in the day
and nobody had GBBRs that are the cornerstone of the measuring problem
So as long as you had the right cylinder to barrel combination, testing on .20s was actually pretty accurate.
But everythings being converted to muzzle energy testing now, but the only way to test it is to measure the fps of the BB you'll be using at the proper hop setting. So you're still measuring fps to find muzzle energy. Difference between testing with .20s is you're not assuming the energy gain curve with heavier ammo is linear, which is the problem.