Hack is ~30% slower then Pig Sticker, and you already have 600% thorns damage per hit from 6 piece. Hack increases thorns damage dealt per hit to 700%, or a 16% increase overall in damage, which is worse then Pig Sticker's 30% faster attack speed. Finally, as mentioned, Pig Sticker rolls with an extra stat slot above other weapons - Hack has 6 stat slots. 1 of them is taken up by a secondary stat, 1 of them is taken up by a power, which only leaves you with 4 stats. Pig Sticker has 7 total stat slots - 5 of them are primary stats, with the other 2 taking the secondary slots - Unlike nearly all secondary slots though, Pig Sticker's secondaries will increase your damage done. While there aren't many Human type mobs in the game, something like 23% of all possible mob spawns in a GR are Beasts, which was likely increased with the addition of the new mob types (Which only added 3 new undead types, with everything else being qualified as a Beast). In addition, 3 Rift Guardians count as either a Human or Beast - Hamelin, Choker, Sand Shaper. I think Binder also counts as a beast, not sure.
So, no. Hack is a decent starting weapon before you get 6 piece, but falls behind ANY dagger once you get 6 piece due to the increased attack speed from daggers over axes.
I'm rank 1 invoker on SeasonHC atm having cleared GR78, did it at around paragon 600.
I feel like, with the right map I could probably push GR80 and I've only got 610 strength from Caldesann's Despair, also as it's HC I'm running Indestructible instead of Finery. With para ~1200 (2200 more str) all geared Despaired (5200 more str) and Finery (15%) id have nearly double the strength I have now which would likely make me GR88+ viable.
So, yes invoker can. The key is basically grouping large amounts of mobs and utilizing Akarat's Awakening. If you don't have 100% uptime on Iron Skin then your wasting your time with that fight and you need to group mobs better. Also getting lots elite packs is a huge plus, getting mobs that have fast attacks and small hit boxes (so you can get more of them around u, the little dagger wielding things from A5 rock) and then the right affixes like fire chains is awesome because it's lots of little hits meaning lots of blocks and thus reduced cooldowns.
Ultimately, like every season so far if you want to push ranks it's really just down to RNG and time input to get high paragon etc. As with any build it's quite simple to work out what it is that you need I.E. Mob type, map, pylon, how to group etc. And you just need to spam rifts until you get the right layout which is kinda lame but that's just the way it is when trying to push high.
So people are speed farming the 70's in just a plain old Invoker set, Dang I must be doing something wrong...
Oof, same here. I can do 65 consistently, but I can't beat the clock on 66. Granted, I don't have the exact build I see a lot of folks using. Maybe I should try harder to roll a good Pig Sticker.
Another question about Invoker builds... is there a hard-and-fast "obvious" choice for armor gems? I thought at first that my main stat would be the clear option (so Rubies), but then I remembered that I get +Thorns for my Vit. So I tried swapping them out, and the Amethysts seemed pretty nice. Not being a D3 mathematician, though, I have to ask... Which do y'all think I should go with?
If that's your gr push build, then it's obvious why you can't do 66. You need Convention of Elements in cube and then simply align physical element buff with Iron Skin and burst an elite down within seconds.
Also you do want the Hold your ground passive. It's not only dmg reduce from more blocks (blood brother: blocks deal 30% less dmg), but also more dmg reduce from Justice Lantern AND a dmg and toughness buff from Akarat's Awakening cooldown reduce from blocks AND from your Invoker 2pc bonus, which gives you a stack with each block.
Also, the 20% blockchance from Blood Brother seems to go over the 75% block cap, which means you should try to reach 95% blockchance in total.
edit: Also, the thorns rune on your horse is not necessary. Invoker thorns dmg is very low when you don't actively attack and push the 2pc buff to high stacks. Longer duration is better.