well I think the point about 'exploiting' is about being able to abuse game mechanics to the full potential with a class that can change the way mobs behave
not necessarily as extreme exploiting as that particular example, but doing things that no other classes can do except pretty much bards and enchanters (and I guess with limited scope druids (charm animals) and necromancers (charm undead, limited mez))
charm - can do some crazy stuff with this... find the right mob to charm and you can break the game. some mobs have ridiculous DPS or hitpoints. for example, you used to be able to charm The Statue of Rallos Zek (I got a screenshot of landing Dictate on him during a raid)
pacification (change agro radius) - can navigate deep into dungeons and lower risk, and until recently 'double pacify' was an exploit that broke the game
mez spells - lower risk, control situations to crazy extent, basically you can pull of some epic hero moments when you mez like 10+ mob trains
mem blur - once again can lower risk, control situations, save the day
song of high sun - amazing bard only skill, once again it can be game-breaking
modify factions through illusions and +faction spells and go to places you're not supposed to be able to go to (for example, permanant illusion AA + minor illusion made you be able to move around North Temple of Veeshan with dubious faction, could just waltz on into Plane of Mischief...)
for example, using a combination of the above if something agros that shouldn't in regular situations it would cause a death or mass wipe, an enc could mez a mob, pacify it, mem blur it, and then it would just stand there and not kill everyone. if mob can't be mezzed (dragons or giants) you can do a root+paci+mem blur and save the day.
or you could charm any unwanted additional mobs and pull them away from the group/raid (or make it fight for you)
or you could highsun a mob and make it go away completely...
insane exploits and abilities, that are mostly legit and within game rules, but nobody else can do! and depending on how well you understand the class and your play ability is, it could be above what the developers ever intended and be game-breaking godly type stuff that sometimes makes encounters have to be re-balanced or things get nerfed/patched
it's crazy good fun
but hey I might be biased towards enc because I've played one since 2001 and exploited the be-jesus out of the game with all the crazy things they can do, such as soloing group-level content and then some
there are some crazy things necros can also do with feign death, invis and divine aura and all their mob-controlling skills (fear, snare, charm, mez)
the point is - classes that change mob behavior = hax city