Probably not deliberate. The other premium helbore skin (Desert Spear) does not have the good sights and the best sights for a bolt pistol are on the free mastery/mechanicus skin rather than any of the 3(?) premium skins there have been.
Also, while you and I think the Legacy of Vraks has a better sight, there are some people out there who don’t agree. When it came up on reddit a fair number of players preferred the default sights instead of LoVraks. I don’t really understand why they feel this way but here’s another example: Refund of "Legacy of Vraks"