Honestly its really what the community accepts to be legitimate or not. If certain tactics or methods are regarded as blatant exploits or flaws in the game itself by a significant majority in the community, then I see no reason for it to be considered otherwise.
There is no official rule book or list of no-no’s for record attempts which results in there being a lot of gray and largely disputed areas among the members of the community, an obvious culprit of this is Fiery Rush. If you consider fiery rush and the amount of obscene (and obviously unintended) amount of damage it does relative to other skills, this could very well be viewed an exploit. But on the other hand, the skill is so widely used as far as record runs go that it has just simply become a part of the meta. Fiery Rush can be compared to so many skills that were blatantly abused in GW1 (NT comes to mind) to achieve faster times that eventually became such a core part of the record scene that not using them would simply be foolish.