I think the thing that kind of bothers me about Operation Mi'hen is a lot of the hindsight issues of the game itself. Sin, is not a difficult boss mechanically. Now, that's true of a lot of FF story bosses, they are not terribly tough by design some of the time and this instance is no different. I think my issue is that narratively, Sin has a weaksause weakness, of which if the Crusaders and Al Bhed had simply known at the time, this operation may have partially succeeded. And that knowledge sort of diminishes the fact this whole sequence is designed around showing off how overwhelmingly powerful Sin is and driving home the false idea that the Final Summon is the only means of beating Sin to the player.