This means that your "In other words" are your understanding of what Tolero wrote. I think you misunderstood.
Perching where the spells of arcanes can reach you puts you in danger. That makes using the perch not an exploit.
It does not switch from being "cheesy" to being an "exploit" just because the arcanes are killed. It is still a legitimate perch and fair to use.
The mobs, unable to shoot or cast back, are not unresponsive. Their response is simply that they are unable to do anything effective against you in that perch and they are too stupid to walk away from danger.
This is the limit of AI in general. Mobs only know one thing. They are not smart enough to recognize that they are in imminent danger and that they have no response. So they don't move away.
It is effectively no different than a beat down of a mob that is unable to scroll heals or drink potions. It is simply a by-product of AI.
In other words, it is how the game works.
If when taking the perch the players are in danger then they are not using an exploit. Eliminating the danger does not change anything.
OTOH, if in taking the perch the players are not in danger and cannot ever be or have been in any danger it is what Tolero describes.
Sorry if that isn't how you understand her. But, if Turbine meant for the "exploit" to not be there they would have removed it. If it has gone on 7 years then that is Turbine's problem and not the players' problem.
If you think it is an exploit then bug report it. If Turbine fails to act in an update then it becomes tacit approval and confirmation that it is not an exploit.
Perches are relatively easy to fix. Simply raising them higher than max jump solves the problem. Unfortunately, Turbine's code is so muddled that simple geometry fixes are just as likely to break a whole quest as to fix something they did not intend.
That too is Turbine's problem and not ours.
TBH, there is way too much fixation on this "exploit" topic. Take personal responsibility. If it bothers you, don't perch. If you're in a group that does, leave. It really is that simple.
And, don't be jealous or spiteful to those who run quests differently from you. If they get completions and you do not, don't blame them. There is always more than one way to get thru a quest. Find an alternative.