currently there is not much difference between a yellow item and a legendary item.

to make a distinction between the two, i would like to suggest to have a weapon mastery gem.
(you can name it whatever u want or see fit what's important is to make a separation between legendary and rare items).

this would allow legendary items to have an affix of: "chance proc, chance to cast, multicast, or auto cast item and so on.." your creativity is needed here. 1 type of mastery gem can only proc 1 type of skill and only 1 gem can be socketed to a weapon.

the gem would be socketed to weapons and that would would have 3 tiers or level. each tier reached by leveling the gem on the weapon increases the chance to proc your made up skill.. example,

tier 1`: 5 percent chance to proc invulnerability for 2 seconds when life reaches below 20 percent.
tier 2: 6percent chance to proc .. [so on]when life reaches below 20 percent.
tier 3: you get the idea.. just some creativity on what skill to proc and what clunkiness irradicate.

these gems should be only for legendary weapon or uniques. and they should be extremely rare. so that only those who put in the time would have it.. makes people see value in it.

some examples on what to proc:
- 5 percent chance to proc a primordial skill while spell casting with a bow.
- 2 percent chance to multi-cast last skill that was casted.
- if player life dropes below 40 percent will cause your pet to activate a healing for 10 seconds when using a shield. cooldown 20 seconds. lowers cooldown per tier reached.
- 2 percent chance to cast Gods Strength (triples player damage for 10 seconds) while being hit and equipped with a 2 handed melee weapon. duration increases per tier reached.
[np need to follow my exact examples.. im just giving an idea to you guys to play with in the future.. i hope you consider this]

i hope you understand what i mean, please play with the idea in your head. i know you can solve this.
you can can have 1 mastery gem per weapon type.. 1 for two handed ranged, 1 for two handed melee weapon, 1 for staff, 1 for shields, and 1 for catalyst catalyst. GUYS PLEASE THINK ABOUT THIS, this is added complexity but you can just add 1 type of gem for each mentioned weapon type forever and players can just choose whatever fits their build.