I beat the game with 39 hours of play time and to my suprise I got 5 stars on the last boss. I really wanted this trophy because I like the lightning theme for my PS3 but was the final boss supposed to be that easy to get. The battles before the final boss(s) were destroying me.

So my question is did you get this trophy/achievement the first time you beat him.  

If your curious: I used rav,rav,sab until he staggered then I used com,com,rav until he died. I only staggered him once. I ussually can't beat normal enemies in one stagger.

I got it without trouble on my first try, but this is largely down to being over-levelled to compensate for the ever-so-frustrating first form of the boss.

You got it in your first playthrough? Damn.  That end form isn't nearly as much of a pain in the ass as the first and second ones, and I think by the time I started the third I was so intent on staying alive that I turtled more than I need to.
 
It's kind of funny how incredibly easy it is to do it when you get near max levels on main jobs after beating the game, though.  It's just like every FF since, like, 7, the final boss is nothing compared to the annoying optional bosses that you have to kill for 100% completion!

Got it first time, Maxed all the main jobs (at that point), and Second Tier maxed weapons for all three characters (however the accessories were basically a joke).  5-starred all of the forms actually.  But whoever put that 20 minute cutscene before the final form deserves to be shot.  (Yeah, you can skip it, blah blah)

Whoever designed the entire story component of the last two chapters should be shot.  It was going so well, why did it have to take a giant crap on itself at the end?

Without doing more than maybe 10 hunts, without leveling any jobs other than the main ones, and with generally pretty terrible gear I was able to get it on my second try.   And I probably would have gotten it on my first if I had known about it.  (I actively avoided spoilers dealing with the end of the game and those trophies)
 
It is actually not hard if you have the right Paradigms set up.

Since it's been forever since I was that low levelled, I'm guessing it just has to do with staggering it as quickly as humanly possible? 

Well, I'm sure another factor is that the time you are given to get five stars is longer when you have lower stats.  So if he didn't max everything out or spend a lot of time/money levelling his weapons, he might have had lots of extra time to cast some buffs at the beginning of the fight. 

Is it really that big of a difference, though?