At 100 TP, Hagun gives 20% WS damage boost compared to a normal D75 GK. (1.875/1.5625 = 1.2)
At 200 TP, it gives 33% WS damage boost compared to a normal D75 GK. (2.5/1.875 = 1.33...)
At 300 TP, it gives the same result as normal D75 GK.
The actual graph not precisely linear (since they are 2 piece-wise rational functions). It's a bit concave from 100-200 TP and a bit convex from 200-300 TP.
Nonetheless, it still gives a roughly correct picture of WS damage comparison.
Its not that it does 'less' damage at 300. It does the same dmg at 300tp as any GK. If you read the scaling and understand the properties of the Hagun you'll understand this.
lol,
If you understand how Hagun works, then you don't need to look at this picture.
And if you don't understand how Hagun works you won't understand it.^^
Basically, all you need to know is: "Hagun is awesome!"(at <200tp)