Want better weapon, do Thordan Ex or A4S... It's that simple.
That's aside from unknown tank re-balance changes coming in 3.2.

They can obviously not put the same stats on all weapons of the same tier.
Some weapons BiS from Thordan, some other weapons BiS from A4S, some other BiS from relic quest... While it results in complaints from people like you, if A4S had all BiS stats and Thordan/Relic had strictly worse in all cases, there'd be much more complaining from people like you.