As someone who wanted extra difficulty, I assure you this is how it works and anyone suggesting otherwise is wrong. Primarch is just ridiculous, tedious, and absolutely beyond unfair. Captain is frustrating but probably doable (in fact, I may have beaten the game on Captain before - I just play through so many times I forget) so long as you're familiar with the game but you pretty much have to min-max squads into their ideal playstyles. Thaddeus is pretty worthless on any difficulty above sergeant because his ranged is terrible and assault jumping into even slightly more than he can handle will likely mean death without great wargear drops for survival.

It's really sad, but Sergeant is absolutely the intended way to play the game because then and only then can you actually use other wargear aside from what's most optimal and build your squads however you would like to play them. Chaos Rising on Captain could be interesting, but still flawed for all the same reasons.

@JmDaFuz Terminators ready.

I played this on primarch "Coop admittedly," and defense missions are not impossible but requires The exact right orders at the right time to keep the enemy forces off balance and HIGH PRIORITY TARGETS DEAD.

Seer councils for example will absolutely demolish your marines with their hand beams. # not eldrich blast.

Same for venom cannons from the nids and reravers devourer cannons.

Basically one needs to be able to read the field and the flow of battle. you cant trust your units to handle it on dps alone.

I ended up playing through the campaign on easy mode, so I don't really have much of a say in this, but here's my take.

Base game, play on whatever difficulty you want, unless you want to get more out of the final mission in the campaign, or you just like a challenge in general.

Chaos Rising though, I'd say you should probably on hard mode or at the very least normal mode for sure, if you want to meaningfully engage with the chaos system.

I played through Chaos Rising on easy mode and I absolutely regretted it because it took all the tension out of choosing or completing purity objectives while reducing the necessity of choosing chaos to keep your team alive. Good and evil simply became choices rather than meaningful compromises or convictions in difficult situations, reflecting the give-and-take in armed conflicts in the 40k universe.

I beat the game on Captain but the one eldar mission where you have to kill the avatar of kaine is impossible to achieve unless you glitch the boss. Most defense missions were easy once you get cyclone missiles, mines and plenty of turrets. Also just use your hero as a tank and kite the big units around or into your mines and turrets. You will die at least several times during mid game until you get terminator armor.

I've beaten this on Primarch Difficulty pre-chaos rising back when it was GFWL. It can be done, unless they reworked the game since then.

Beat the game on Primarch without Cyrus exploits, all buildings, minimum downs and no defeats.
Primarch is tedious, frustrating and extremely unfair. Even if you're great I only recommend Captain, and only only on your second play through.

@M1873 Gaming You don't get better gear with increased difficulty, it is fully randomized, at least in the base game.

The defense missions its possible to get the shrine over the other side of the map using the scout and a specialised grenade load out. But not easy. Defending with 3 is hard and you will need extra turrets.

Make the tactical squad into a hand to hand squad,use the dmg reduction skill. This squad is a monster in hand to hand because it has one more member and many slots for grenades. Make commander heavy weapons, rocket launcher works well. The scout squad can solo most of the tyrinid missions, particularly the early desert map ones. The second half of the game is more difficult its true but the real challenge is beating the level without dying on primarch and as posted below there will be alot of running away. :)