This goes back to a very old circular argument ever-present in XI.

Nothing in the world is black and white, and the same holds true for the MMO world as well. People have varied opinions; however, the group who decides whether something interesting is an example of exploitation vs. smart optimization is ultimately SE and SE alone. We as the XI/XIV community argue on the forums, but we all have varied opinions. The only one that matters is SE's b/c they are in charge of game balance. If they deemed this BLM burn idea legit, a lot of people would be frustrated, but it would be legit. Best example I can think of for this is Utsusemi tanking in XI. Far more broken than half the stuff they deemed exploit in XI but they let it be and it became common / required strategy.

To the minority of the community that actually pushes and comes up with these crazy min-max ideas like the BLM burn Garuda idea, it's not about some raging philosophical argument about game balance and exploits - it's simply about min-maxing and pushing the current mechanics of the game. We do, then let SE decide if this is exemplary strategy vs. an exploit needing a patch. It's a very necessary aspect of the community because SE cannot be 100% in catching these in testing. They rely on players to push the boundaries, then they react accordingly to preserve game balance.

Now to play devil's advocate here. The real interesting philosophical discussion here should not be if this Garuda burn is an 'exploit' or not, but instead how would you feel if Legacy had done this, hidden it and farmed the crap out of it at their leisure for 3 months, then told everyone? Now that's an interesting discussion. Spoken like a true XI LM-17 I guess.