well i would hope that any experienced gm should be able to see when something is overpowering, and not being used as intended.
And i would say that stun locking a high lvl monster, so that you can beat it without a scratch, even if the challange is a few levels below you, should not be possible. The first time my players would do such a thing, i would drop another wandering encounter on them. And then afterwards i would make a house rule.
Just as when the paladin mark first came out. I sure read about the ability online, and sure enough, my players immediately caught this flaw, and wanted to abuse it. You tag it and run away.
But you are the tank for crissake... ac 20... and you tag and run away... now that's working as intended..

thankfully i stood my ground and made a instant house rule addition.(already had house ruled it, but not well enough)
thankfully they came with a perfect errata for that ablility, and i guess they will for alot others too.
Just because it's in the rules, doesn't mean it's right. They probably just didn't have as much playtesting at higher levels as the low ones.
In the end, what it comes down to, is that if you as the GM feels that something is not working as intended, it probably isn't.
Feel free to modify it instantly, to avoid any game breakers.
Because as a player, most people will grab anything they can get.