Invoker's set lacking key stats

While this set has been buffed multiple times and the recent changes to it are interesting, it’s still very hard to make a good build around it because it’s missing some essential stats.

1) It takes up two important slots in the amulet and offhand
Besides the head and weapon slots, these are some of the most important slots because they can give +1 to both masteries or massive defensive stats.
I really think this set should have at least +1 Arcanist as part of the 4 set bonus so the above doesn’t hurt as much.

2) Set gives only a small amount of OA and no DA
For a 4 piece set to only grant 60 OA just isn’t enough, which means you’ll struggle to reach viable OA/DA values in the endgame.
The set does have 150 Reduced DA, but considering how it focuses the damage types to Lightning and Fire it’s clearly tailored toward a Sorcerer build which gets the same debuff from Flashbang.
Perhaps it’s an idea to change the -DA debuff to a stacking one to broaden its usability.

What compounds the above issue is that while the set steers you toward the Sorcerer combo, neither mastery gives any DA which means you’ll end up with a low DA value like 2200-2500 with typical top items for this kind of build.
The set really needs some more OA, added DA or other defensive stats somewhere, especially the 2 and 3 set bonuses are lackluster and could use a boost.

Trozan’s got a nice buff recently, it’d be great if we could get the same for PRM.