We have several fights in this game actually that punish you for having good or well geared DPS players and/or excellent healers/tanks, mostly old ones. And the big question is: Why exactly are you punishing players for taking part in the vertical progression you offer and why exactly are you punishing players for playing their job well...?
With all due respect: The notion is pretty perverse. You should reward people for playing their jobs to the fullest and gearing up, not punish them for it. It should make fights easier, not harder as you suggest. It doesn't even solve the issue, because the meta for those fights doesn't become to take it slow, it's to go full speed until you hit the stop sign, wait, then go full speed again and rinse/repeat until you can safely full speed to the end.
It just seems like a helpless attempt to achieve something without addressing the actual issues.