The thing with exploitation is, its impossible to completely stop, you can't predict every possible loophole players will find ahead of time nor can you see every unintentional design flaw. Its a part of gaming of which all players are accustomed to - whether it be knowing a particular spot a boss can't AOE in, or running tight circles around objects in pvp. Many exploitations are embraced and often turned into interesting features in the future.

As far as speed runs go, none of those dungeons were tested in the beta - they were bound to have a flaw or two, as far as I've seen monsters don't generally heel in many other dungeons.