I figure most competent DDs will arrive at a timing scheme like that just from knowing when a cooldown will result in wasted uptime or death. It doesn't invalidate potency per second math at all; "All models all wrong, but some are useful."

Using cooldowns on cooldown is raiding advice that comes from years of MMORPG experience predating this game, I've been told. It shouldn't be understood as a key to optimal DPS, but rather a reminder not to waste opportunities.