They pulled the same stunt with 210 equips during 210 content? Which, like I said, was complained about just as hard, if not harder, than these 280 weapons? Despite being on par item level with upgrade tome gear? That's why I say even at 270 these threads would exist, because that's on par with upgraded tome gear, which was the complaint about 210 equips.
Also, people would complain about it if it came in june, because we're still be in Heavensward. People wouldn't complain about if they did it after Stormblood, because people would go, "What's a Diadem?" on mention of it. I can tell you after we got 230 gear there were people that forgot Diadem was a thing, even after complaining over 210 gear like it was the death of XIV.
You bothered with it because you thought it was going to be BiS, despite how in 3 months it would just be glamour. Again, if you are upset, honestly crying at the keyboard over it, you can leave. Your sub, not mine, I can't make you stay. However, you're missing a specific thing.
Nobody, and I mean NOBODY in the entire game is going to leave you out of content for not having this Diadem weapon. Unless it has a cool appearance tied with it, everyone is going to forget about it in 3 months tops. Meanwhile, for 5 less, you got a questline to watch a weapon you nurtured grow, from a small little 170 weapon looking exactly like eso gear, to a unique, beautiful, glowing model that shows your determination with the achievements and bragging points to back it up. This is also coupled with the fact that because you did your anima, the Stormblood version will allow you to obtain an advantage that anyone who didn't bother to do won't obtain, and you'll be able to use this item still for some time afterwords. In fact, I bet come Stormblood, you'll replace both of these items on the exact same quest, showing how little of a difference it makes at the end of the day.
Honestly I'm surprised you didn't quit when they nerfed all the steps you completed, considering that wasted your time too since anyone that waited didn't have to do ARF 1000 times like you did.