I would say if it's too hard change the setting from normal mode to story mode (I did not know this until end of A2) that there were 2 different difficulties for campaign mode. Once I did that everything became 50% easier.

If you're already in story mode not sure what to tell you.

Yes, not only is it possible, it's friggin easy.

When I got to the Act 1 Boss, I had the following active skills

Winter's Grasp? (Aoe frost)
Bulwark of Dawn (Damage modifer taken)
Hunters Swarm (3 minions)
Feeders Swarm (3 minions)
Livor Mortis (Mostly plus health and increase threat)

At this point most of my points were in Toughness (Near 200pts, I had started building wisdom at this point, they're about even now), I had A LOT of HP buddy, but it didn't matter, the boss almost never hit me due to the golem holding aggro THE ENTIRE FIGHT. (Golem never died either.)

I put the golem on the boss and hit the active skill again (The golem will roar, I think it's an AOE aggro move, but I have no idea). Started moving around the boss and keeping my Bulwark up on him as much as I could, since it did most of my actual damage from me. Freezing whenever I needed it. When he's away from you, do some auto attacking to get the rage gone and repeat. It works for all 3 phases.
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I also cleared the Act 2 boss with the same build, same minions and same strategy, though, if you haven't been there, you'll see why being smart is more important than your minions during that fight.

I also created a b-line between the starting passives and the "summoning tree" where I systematically picked them ALL up.

Minions arent currently underwhelming and this is an understatement they just plain out suck... the only decent minions are currently Livor mortis and parasite if u catch a big Boi such as a tormentor/frost tormentor other then that u own your own dealing the dmg

if you go a poison summoner build and use parasite as your single target damage you fly through the game. and ive been doing expeditions quite easy as well. the sooner you get the tanky minion nodes at the top of the plaguebearer tree the better. and you just use plagueburst ability + the passive poison applications in plaguebearer tree to clear the trash mobs.

Concur.

I raced up to the summoning tree, filled every slot; grabbed Plague Burst (replaced Winter's Grasp with it, and replaced Bulwark with Parasite)

Once the poison clouds start going out, everything...and I do mean EVERYTHING gets melted. If you want a good laugh, snag a Necromancer that raises Frozen Husks with Parasite....which basically gives you a WALL of corpses between you and enemies, and nothing but noxious gas everywhere.

I'm running basically the same build. The boss in act 2 is giving me a hell of a time. My minions just don't attack it, and I don't really have any other source of damage. I burn through all the other content though. It is pretty rad.