When it was initially introduced back in Mists of Pandaria for the Throne of Thunder raid, (thunderforged) it increased the item level of a raid drop by 6. It was one of those things where it was neat if it happened, It wasn’t game breaking and you didnt feel bad if an item didn’t.
Fast forward.
-An item drops from normal, and has a totally random chance to upgrade to an item level that is on par (or better) than a heroic or mythic piece and yet takes no where near the level of difficulty or execution to acquire it… lolwat?
-You finally get a drop you’ve been after and it feels good. Then you notice that the item didn’t randomly get an upgrade and you feel kind of bummed out and think “sigh, it COULD have been better”
I believe the whole “random forge” was originally meant to give you/your guild group a little extra oomph on gear drops to get past an encounter you were stuck on, not blow past it
As far as corruption goes, it’s an interesting system in that you can swap effects around on gear based on the kind of fight/content you’re doing to be more optimal. Unfortunately, it is not without its flaws, one of the biggest being the same issue that the legion legendaries had: getting one, but it wasn’t one of the “super good/amazing/op/broken ones” which made it feel bad to get and would put you way behind on the meters.
Some ways it could have been improved, including but not limited to:
-Better balancing of the effects
-Some modicum of control over what effect you get and/or what piece of gear it is on
-Incorporating crafting professions
-Being able to remove corruption 1 rank at a time, instead of removing the effect all together