People are crying about this because they derive pleasure from being on top of the pile and being able to piss on the unwashed masses who don't have an Allagan weapon.
Turns 1 through 5 of The Binding Coil of Bahamut will become, upon the release of patch 2.2, deprecated content. No longer current. No longer bleeding-edge. It is a soft progression reset, and the tryhards are none too happy about this because they are losing their "specialness."
Your logic is flawed. If someone can't win at the current difficulty, can't progress beyond what content we currently have available, what do you think they'll do?
Don't worry, I'll answer that since thought is clearly a foreign concept to you: THEY'LL STOP PLAYING. And Square-Enix will lose money.
I don't consider myself a "hardcore" gamer. I don't even log in every day, and my company is still wiping on Twintania while I see lots of people walking around with Allagan weapons. Now, I would like to get a Twintania kill before she gets nerfed, sure. That would be cool, because I'd like to finish the encounter at its originally-intended difficulty.
However, there are people in my company who are nowhere near killing Twintania. They will not be near killing Twintania when 2.2 drops. They might have just started playing the game. Or they may not be as skilled as other players in the company. Or perhaps they can't log in regularly enough to attend scheduled Coil runs. Or maybe they live somewhere with poor internet infrastructure. You can think they're useless, you can think they suck and you can even hate them all you want; they don't know you and likely don't care. But they pay their subscription fee and they deserve to get to experience the content, too.
You just get to do it first. Unless you intend to start paying the subscriptions of everyone who quits because they're locked behind four deprecated tiers of content and can't find anyone to help them clear it when we're on patch 2.6, then you really have no room at all to talk.
Additionally, I honestly believe that the people complaining about this issue have some serious psychological issues if you need fake accomplishments in a virtual world in order to make you feel good about yourself.
Yoshida outright stated that he designed the gear in XIV this way on purpose with the express intent to avoid having to farm up ten sets of gear to clear one raid dungeon.