The 3oC exploit is not an exploit at all.
it is working as intended with a level of chance.
So what if Gralyx is readily available, it is the same level of farming as You Have Awoken The Hive.
I don't see it as an exploit
It isn't an exploit, though it's not really comparable to farming The Dark Beyond because of the enormous gap in terms of payoff for time invested.
It's "cheese"; the abuse of intended mechanics in an unintended way, and rather cheesy cheese at that. It's incredibly obvious that Bungie did not intend for people to use
multiple coins per minute consuming hundreds of coins in the course of a day. Shooting the Oracles all from up top to not have to deal with adds, burning Vanilla Skolas in 15 seconds to bypass all the mechanics and hiding in the little safety box for Valus Ta'aurc are also cheese. The coins are functioning as designed and it's absolutely Bungie's fault for not seeing this potential abuse of its properties coming and coding around it. No one ever need fear getting banned for cheese, but it's certainly the sort of thing that's patched out now and then.
An exploit is instead something that takes advantage of something unintended, potentially in the vein of a bug or reproducible glitch, usually only in the game by accident, to gain an advantage. The heavy ammo glitch, harmless as it may have been, was an exploit (though one provoked by a huge bug in its own right). Unplugging your ethernet cord when Crota kneels is an exploit. At their worst- what we'd call malicious exploits- these exploits give an active competitive advantage over other players. The original heavy ammo glitch in PvP is an example of this, and is the only well-known incident that resulted in targeted account bannings by Bungie.
There can be a lot of differences between the two in terms of difficulty to fix and priority. Exploits are usually more severe problems in need of rapid adjustment, but can involve completely unforeseen variables. Fixing exploits also tends to be risky toward other things; move a part here, break something else there.
With something like the 3oC thing, Bungie can easily see how and why it's happening according to their intended design. They need to do some additional work to solve the issue though; I'm glad they didn't pull them down in the meantime.