I found DoW II easily exploitable. Learn the mechanics and see how the enemies react to certain actions of yours.
This is what worked for me:

Squads: Commander, Tarkus, Avitus and Cyrus (incredibly broken!!)

Commander tanks. Go full hp early on and choose equipment accordingly. Shielding ability from commander crown or whats-it-called and med-kit to revive/ elongate tanking phases to establish a stable frontline. Also use orbital strike with him for boss cheesing. During mid-game spend points on an additional equipment slot, but priority is on hp.

Tarkus: Go a little bit tanky in the beginning and then go a little bit distance damage after that. Give him an additional slot, as well during mid-game. Try to go the energy tree, so that the defense bonus affects all squads in the late game. Equipment should boost distance damage. Also equip flash-grenades, usual grenades and melter bombs, if you want to destroy vehicles faster.

Same goes for Avitus basically. Equip with rocket launcher for good damage and additional crowd control. Your main source for damage. Instead of going full energy, you should go with full distance damage in the late-game. Give him this invincibility thingy from the shrines.

Cyrus: Level energy until the one checkmark before the last one, so that he can use equipment while cloaked. Max out distance damage for enemy debuff and get explosive shot in that tree pretty early on. Makes picking the tyranid elite and the eldar damage cannons out very easy.

Defense missions:
Early to mid-game only bother about defense missions on typhon, that are about protecting shrines (ONLY on Typhon, dont waste your time with the other crap.) I noticed, that these defense missions scale with campaign progression. Dont bother trying ANY of them, however, in the late game, because the scaling is just off on this difficulty (even so on captain). Don't waste your time with it. You'll be wanting 4 or 5 shrines secured for the last boss on typhon.

CHEESE bosses:
Go cloak with cyrus and go near the boss. Throw an orbital strike on it with your commander, without getting all too near. The bosses seem to just chill in their cozy spots when not engaged. Spare as many of the explosive shots with Cyrus as you can for the boss. Dont pick up unnecessary crates, for they'd be wasted. Stay cloaked and shoot away, until they die. Some bosses, as the eldar ones, spawn in additional mobs, that are obligatory to defeat, I'm afraid. Fall back with Cyrus and let the rest of your troops kill them, using full agro tactics, all the while utilizing Avitus' invincibility thingy to keep your troops up. Watch out, that your commander engages them in combat, so that the rest of your troops can fire away, use both Qs of both Avitus and Tarkus and the W-ability of your commander. When these troops are done with. Go on with the Cyrus stuff until boss is dead.

Many people seem to have stuggled with the second time you fight this one eldar b**ch. I failed there once, too, because I made the mistake of capturing the beacon right next to her. Just ignore this one and keep the last beacon as retraction point, she wont be following, neither do her minions.
In this special case I also noticed that orbital strike + 5-7 high-explosive shots might not be enough to kill her completely (ALSO: don't go out of her view, she'll be teleporting and youll be making this much harder than it needs to be).
I might have been lucky on this one, but I found myself being able to recreate the following:
So I cheesed her as mentioned, but additionaly, while staying in the exact same spot with cyrus, I threw explosive charges at her, which she didn't seem to try to avoid. This was enough to kill her in the end. She once shot at cyrus, but didn't seem to care too much after that. I was cloaked, too the entire time, except not really, because she seems to be able to uncloak enemy units. I dont know, if this contributed, but I did it anyway. Dont move cyrus manually after a certain point. Just move him near the corner near the building and aim with explosive shot on her, so that he moves on his own to take the shot and leave him there after that.

More general tips:
Assign numbers to your squad with Ctrl+{1,2,3,4,5...} and select between your squads by pressing only the assigned number after that. LEARN special ability shortcuts. You won't always have time to click on your units and use special abilities with your mouse.

The last mission is relatively easy. Just do your defense stuff. Use explosive shot for tyranid elite distance fighters. Use your special abilities in the right moments, throw one or two flash grenades, if you feel that you could be overwhelmed soon, but try not to move your squads while doing so. After that just capture the beacon. Bait the boss with cyrus to pass by his invicibility phase and then fully engage with all your troops, while being ready to pop the 4-5 invincibility-thingies that you should have left. Make sure you don't waste them when you use them too early. All buffs and debuffs activated fck this guy up. After one or two uses, if you feel you might get overwhelmed, press "x" to retreat with all of your troops. When all charges are used there should not be much left of his life. Do the rest with orbital strike and high-explosive shot, while cloaked. (There are many, many crates in the final arena.)
Also make sure that cyrus sits somewhere in the back during full engagement phase, being cloaked, in case something goes wrong you don't wipe and can revive your squads.