[DEV Question] Why is this allowed?

[Reynhart]

Mmh... not sure if I like that tbh - while I do see the problem here with questlines like the relic and weapons being the ultimate reward from raids I can understand that they're giving the most boost when it comes to damage - just like armor gives you more HP/protection for incoming damage. The weapon is what deals damage, the rest of the gear is what protects you - seems pretty intutive to me...

Weapons could give something else that pure damage. That's pretty much what people requested for the Relics since 2.0. And it would introduce an interesting customization as you wouldn't automatically chose the highest ilvl weapon.
And, frankly, no one really cares about "protection". BiS is determined by what gives you the most DPS.

And its also a bit more "interesting" - we dont have that many choices in the game after all, but if every piece of gear basically does the same those options get even lowered when it doesnt matter if you get a new weapon or a new bodypiece.

That's still not a choice. Like I said above, in 7 weeks, you can earn 3150 capped tomestones. However you spend them, if you want to increase your DPS the most, you buy the weapon.

Had a tank in DV recently, best accessory was a level 39 earring, everything else was way below.

lvl 39 as best accessories is really pushing the undergear to the limit.

Through some SSS dummy work using i110 Glanzfaust and i110 Gloam Tabard I found that I did 1600 dps with the weapon and 2400 dps with the chest piece.

That's my point, the gap is too much considering the cost of both those items.