Thanks for giving me an excuse to play the campaign again :)
TL;DR: Don't worry, it's normal to be stuck, the game is complex, but at the same time: there are a lot of ways to win. Mission help after introduction.
Intro
First of all: Don't worry about the forum messages telling the game balancing is broken. Second of all: Also don't worry that you are stuck. The game is complex and has some serious design flaws.
The game balance is not broken, it's just a lot of Rock-Paper-Scissor esc. Counters. I did a successful "no safe scumming", "no rune scumming", "all campaigns" run on hardest difficulty and only needed to reload a campaign map two times (White Lord). Could probably run without Artifacts as well, but they are most of the time my backup strategy against bad RNG, so i probably won't.
The thing that discourages most, is that you need to approach the game as a multidimensional puzzle: you got resource management on the strategic level, choosing the right opponents at the right moment, efficient map movement while juggling that with building an efficient and reliable card deck - with a card metagame that can rival some MTG formats.
It's simply too much right from the get go, and that's ok to recognize. I got both experience from HoMM and Civilization on the overmap part, as well as years of MTG tournament experience, which makes the combination fun for me.
But the first step should be to think about, what you might have missed and improving on that:
* Beating an opponent in a fight seems impossible? Maybe you brought the wrong deck/resources, because you didn't use everything the overworld offered
* The card battling portion seems to be too random? Aside from the starting decks (can't change them, and the Kinets starting deck is by far the worst concerning RNG dependance) you can build decks for consistency and should do so.
* An opponent seems to be a road block? Have a look around the accessible card shops - maybe you missed a specific counterspell for their strategy. Good examples that often get overlooked are Enchantments, Spot Removal and Enchantment Removal
One major design flaw exists: Losing your hero after a defeat. If they got resurrected at your castle everything would be fine, but losing them is simply too much resources spent. You can build strategies around that, but Etherlords 2 simply manages that better with the RPG concept. So don't feel bad about abusing Save/Load on your first run through the campaign.
Now to the interesting part for both of you: Short walkthroughs of the Missions. I hope i got the correct ones and try not to make it step-by-step so you can find your own way, but if you need more help simply reach out.
Evil Campaign Mission 4: Synthets vs. Vital & Kinets
To be honest: sounds like you already managed the hard part - making sure your ally survives. If the Kinet is Road blocking you, i always went with the top guard tower close to my base to invade theirs. Their Lvl 6 heroine relies on spirits and gibbeling which dies heavily to a gas based strategy with mechosaurus. Remember that Gibbeling don't get up after being forced to rest with your 1 ether spells. I attached a screenshot of the deck i used to kill their lvl. 6 with a lvl 4 of mine. I got the Ring of Paralyzation as a backup artifact against bad draw luck, but never needed it. Also don't overlook that you can recruit Veterans (Lvl. 3 from the beginning) in this mission, the level advantage helps a lot!
Good Campaign Mission 4: Vital vs. Synthets & Aviaks
If i recall right, you don't really need to get the runestone - that's just the direct way. On the bottom of the map you have a longer but easier path that one of your heroes can take to clean the Aviaks. Another way would be to defeat the Synthet heroes - i don't recall having any problems with that using a simple Treant regeneration deck. You just need to get Ether Acceleration (pay 1 Ether, get 3) to be faster than their decks. The map is quite big and forgiving, just don't rush too fast. I easily used the first 20 days just to farm and clear the way to the middle.
Evil Campaign Mission 2: Chaots vs. Kinets
Creature Removal is the key - you got probably the strongest Removal Spell in the game in the spell shop right behind the Lvl 3 Iron Mechos: Polymorph. It destroys an enemies creature for 1 ether in exchange for a few of your life points. Best thing about it? Only the first cast hurts, when your life is already low, it can even work as life gain. Exchange a few Zaps with that, and all fire waves with Kobold Shamans and the Lvl. 6 Kinet stands no chance, as he can only damage you with creatures -> that die to a single polymorph. Take care about the Regeneration of the Warrior Spirits though, you don't have much room for mistakes.
