So, Xur is selling Arbalest.
Big deal, right? Well, I think it is. Here's why.
We had to go through a seasonal event and meet milestones to earn it. The reward was the incentive and the gun was unique! It should be a reward for those who took the time to earn it.
For those who saw the whole event as too much work, they can just buy it from Xur now? That cheapens the event, the reward and future events that offer unique rewards. Why bother, if you can just purchase it down the line, for no effort what so ever?
Why not re-release it with a new set of requirements? Make players earn it like we did? That, or start selling malfeasance, thorn, world line zero, raid gear and all the rest while you're at it.
If this was always planned and the event just got it to us earlier, fine (my bad in that case) but I'm way less likely to grind future events if this kind of thing continues.