Revamp of Rarity and Key System

This idea is to remove keys from being the main form of getting the best weapons and just make it a way to get the basic form of that weapon.
I'm suggesting to make bosses and mobs drop weapons with random stats within a set stat range and the average percentage of the stat will determine the rarity of the item, this means all shops, gift and chest items will have base stats (0%) and players will have to farm a specific boss or mob to get the best form of the items they want.

An Example
Common: 0-5%
Uncommon: 6-11%
Rare: 12-17
Epic: 18-22
Legendary: 23-25

The stats that will be affected by this system will be Base Damage, Attack Speed, Critical Chance and Stat Requirement wherein all will go up and stat requirement will go down.

Example on how the system will work, when an item does drop and all the stats are randomize by percentages what percent will determine the the rarity.

Stat                                      Base Stats              Percentage Increase              Final Stats 
Base Damage                      30                                  10%                                     33
Attack Speed                      2000ms                         25%                                   1500ms
Critical Chance                   20%                               0%                                      20%
Stat Requirement             100agi                            5%                                     95agi

As you can see the Attack Speed got a legendary roll but when combined with all the other stats its a 10% boost and the rarity of the weapon is uncommon.

The purpose of the rarity can be for many thing, one of such can be to give crafter's upgrades a percentage buff when upgrading a rarer weapon base on the average stats percentage.

A way to balance off the economy because the game will have lots of new loot that will have a price on them which is to make the items bound on pickup and they are only able to be unbounded by going to the key NPC which can only be unlocked from Faction Wars, A player will have to pay a large number of berries (like 80% or so of the item selling price) to do so or sell the item for a set price of 500 berries to an NPC if its selling price is more than that.
 

The point of this is to give players a reason to want to keep farming bosses and mobs to get the best form of the weapon they want and not just stop playing when they get that one weapon from a chest also its to remove the importance of keys and make players work hard for what they want by farming the harder bosses and not the weak ones or pay a lot for berries to get that super rare item because the person that finds the weapon will have to have lots of berries to unlock the item to sell it, makes it so berries now have a bigger part to play in the game.