In my opinion, this is the worst thing happening in the game.

Type charms give you double the chance to get, let's say boots.  So instead of 1 in 6 it's 1 in 3.  Combine that with wanting speed (also 1 in 6) then you got a chance of 1 in 18 to get the desired boots.  

That is just too low.  Why not make sure the charms give a 100% chance on giving what you want ? You still would need multiple rolls to get the speed or desired substats.  

Now every doomtower level that rewards charms, feels like a level with no rewards.  And the only time i use the forge is for quests and cvc.