Why? Seems like it causes unnecessary confusion. This can stack with this but not this… it’s just ugh come on, man.
Is it so you can’t stack it too easily? If that were the case, just reduce to compensate, while keeping the overall reduction available the same.
I mean look at this mess, lol: http://i.imgur.com/nkmlaHA.png
Math, it’s good for you 
Welcome to GD where there are tons of “types” of everything.
Took me 5 minutes to understand that chart. Not exactly rocket science.
So having to consult a chart to understand game mechanics is good game design? Cool cool cool.
At what point during the game is a player who is stacking two types of similar but different resistance to know it’s not benefiting them?
There’s not even a loading screen tip. Maybe they could make this chart a loading screen image.
Took me 5 minutes to understand that chart. Not exactly rocket science.
You’re a douche.
The point isn’t whether or not this chart makes sense to you, but that this isn’t good game design, because these difference are not communicated to the player within the game. There isn’t even a loading screen tip about this stuff. You could take Serpent and Eldritch Flame and never know one of them isn’t benefiting you. You wouldn’t even know to ask. So that’s 4 devotion points you’re wasting.
I think it’s unnecessarily convoluted.
There are multiple types of resistance reduction exactly to let you stack some of them, and restrict from stacking others (so stacking RR wont be too easy).
It uses a simple mechanics - effects from SAME sources dont stack (only strongest takes place), and effects from DIFFERENT sources stack. Resistance reduction effects with their own duration apply specific debuff, which is the same regardless of what skill caused it. So, every application of that debuff is considered “the same source” and dont stack. There are 2 different resistance reductions that work this way (flat and percentage), obviously, they apply different debuffs and stack with each other.
Resistance reductions without a duration (spelled as "-X … resistance) are a part of their parent debuff, so for different parent debuffs, whose RR effects will stack.
It’s not SO comlex as it may seem at first glance.
TQ’s heritage. You’d be surprised, but just straightly replacing everything with -%rr type is impossible.
Flat was supposed to be only as a weapon modifier. It pretty much requires a unit that’ll perform a “hit”.
Same for %rr.
-%rr requires a “buff”, pretty much why it’s abundant on procs but non-existant as modifier on a weapon.
E.g. what replacement of flat rr with -%rr on Wind Devil means behind the UI: WD “attacks” targets and Raging Tempest added flat rr to attack. Now it works like Veil of Shadow, which places a “debuff” in the aoe around the carrier.
I’d want rr system to be simplier and more intuitive, but it’s a serious rework. It’s more of a technical issue rather than design decision.
I actually enjoy GD’s RR mechanics compared to TQ. Flat RR was rarely enjoyed by pure spell casters in TQ because of its reliance on being applied by a weapon hit/skill. Now, there are actual spells that apply this flat RR
Besides the fact that you can’t funnel flat from every piece of your gear on your weapon in GD, mechanics themselve are more or less the same. It’s just TQ haven’t used flat for skills. This, by the way, made rr appear more orderly in TQ.
