1. Life leech you don't need for charms, because you can just use potions. It is good for farming, as it makes it more "lazy" characters heals on its own, so you sacrifice some other stats to get that leech. For charms you want take every edge and don't mind compensate lack of healing with potions. If you want heal, it is little tricky with runemaster because you don't really have space for LL jewels, and weapon will not exactly fit many mo, plus you need AR.
2. AR comes from: daedalus (smax), charms, those few jewels you have if you use runeword, and MO in weapon. SU has obviously less mo space than tiered unique or craft, so this is a problem. You want lucky that weapon and put ar mo. Your ar is still too low, you must be missing some crucial charms.
You don't want to use amethyst, only runes, only exception is a runeword then you have few jewels, but I wouldn't more than 1 runeword in entire gear, if I'm going runemaster.
3. If you use better gear, best boss dps is ancients hand (crafted helm), same as iceburst but 35% wdm (so ~40% more damage). Going for lightning pierce and yaggai, it could be worth to max tgod for more +lightning damage. Unfortunately you can't use it with stormblast which would make you deal pure lightning damage and maximize pierce. I''d use it with whatever, deathgaze doesn't work against every boss (astrogha) because it kills totems.
But despite all these problems, yaggais is wayyy better than t6 axe.
For overall best heroic twinked spec, I'd use dual swords, probably 6x fire rw offhand for -60 pierce, as good as possible main hand (xis shark in ethereal kriegsmesser for over 700 damage), ancient's hand helm, every slot with pierce to stack 170 fire pierce, and then be able to utilize whirlwind and AH without weapon switch. It will beat even double damage 2h axe if you could get one (you can't), because of how much more annoying moving around is without windform. If you get access to xis runeword, you can reduce the gap between 2h and 1h weapons damage, because of runewords like xis tal. You get +max damage on 1h that normally is restricted to 2h.
Here is example of very good axe craft for iceburst (no lucky not blessed, with bless can go to -30 cold).
In reality it is still much worse than 1h sword combo because of whirlwind lockout to 2h axe.