Wow, you happily call everyone else all the names under the sun, but if someone calls you on something you've said (something that was incredibly stupid) you do your nut!
No, the mobs seem the same to you because you don't understand the differences. I'm guessing at the moment that you're new to endgame, which probably excuses your ignorance about the differences in the mobs you're talking about. The differences, particularly between Fafnir and Tiamat, are among the most significant in the game, and they've changed the way all endgame NMs are fought.
When Tiamat was first introduced it wandered free, unkilled for months. Fafnir/Nidhogg was killed everyday, and you'd think that Tiamat would die as soon as it popped each week, right? Wrong. LSs went in with the same tactics that they used on Fafnir (hey, it looks the same right?) and they got mashed. The same tactics did not work. It was months before the mob was actually killed, and months more before it became routine.
At least five major tactical changes came about from testing on Tiamat, new tactics that hadn't been seen in endgame (I don't have to tell you what they were, you surely already know). Tiamat even completely changed the role of one job, from a buff provider/back up healer to an endgame DD (until a new piece of gear made it obsolete again, you know what that was too, I'm sure). Tactics that on the surface appeared to be rubbish, and had already been discounted, but tactics that a few players with vision developed changed the way all endgame mobs are fought.
Other mobs have had an influence on endgame tactics, but no other mob has forced a revolution in the way we fight endgame mobs like Tiamat did, that same Tiamat that you see as exactly the same as Fafnir.
It's an insult to the leaders of the top shells (including yours and mine) to completely slight the way they changed the game, and it's the height of arrogance for you to think that because you can't go in and kill a mob with your standard 18 players that it must be broken. You keep going using the standard techniques that have been handed to you, and leave the exciting stuff for someone else.
But hey, it doesn't matter if you know what you're talking about, right? So long as you insult the most people, you must be right...