Formas aren't that big of a deal, you can farm stuff for sale easy, buy a forma bundle per 1-2 days, that's 3 formas for 35 plat, craft 1 per 24 hours with the bp-s from relics, and you'll have a ton pretty fast. The other stuff like the arcanes and the plague parts aren't that much better than what you can get otherwise, you can make PRETTY strong stuff with normal zaw parts, and I haven't even mentioned the best-in-game heavy blades like the Gram Prime.
It would make it a bit easier getting these, and if they redone the mechanics of the event boss and make it at least a bit harder (and/or more fun), it wouldn't really change the prices. It would be a bit of convenience for hard-core farmers, and would make it a bit easier to get a plagued zaw, which is like isn't that big since there are far more powerful weapons anyway.
While it is good to get events which reward good stuff, the POINT is that this gives rewards ALL players find useful, engagement would be high, and it would not be a pointless, and annoying event like the Ghouls making Spacemom filling your inbox with spam.
From what we seen with the new Orb Vallis event, they are willing to make these kinds of events, and since they ARE remaking PoE, we can hope for stuff like that.