QWEEDDYZ: Well, my IMO it opposite most disadvantage of the game. Trying to be like Wh40k canonical game...
As for AI. Agred with that one. For pathfinding feature that... hmm... units moving in large groups try stand far away from each other. Maximum population army by one move command will spread across half of the map. And so for AI in Dark Crusade and SS.
For AI opponent it was better for DoW+WA.
No else disadvantages i guess. And if you ok with small armies battles tabtetop-like - DoW should be good for you. Including WA.
Another disadvantages is enemy are not limited at same level It have at least two differ bases with separate unit limits. But again that going worse in DC and SS on hardest difficulty. Its just skirmish maps when you are one army against two.
As result it is not lore-canonical for Wh40k. And not even tabletop canonical. Whaever faction you chose you deal with more populated enemy. Eldars overwhelm Imperial Guard, heh.
But that my opinion a bit differ from your one. I think this small armies - which one indeed main idea of original DoW - is disadvantages and DoW2 bring it worse. For people who like original idea DoW2 are better. Anyway campaign there more casual.
So for me WA looks like some mods that increase armies. Still limited for player. This one 4th mission if you play as Impire you get allies bases so increased army. But going worse to the end of the mission.
Best solution was in Warcraft 3. There is one mission in Wc3 Expansion allow to use multiplayer mechanic to control allied base.
And Winter Assault bring same feature to Dawn of War. There even more in game engine.
So debug mode or cheat-trainers allow to do that.
Dawn of War 1 try to be that small\average armies tabletop game. But it wasnt. Not DoW, not WA DLC, not DC and SS. Sooo... Khm. DoW is a bad designed game...? Maybe we did play it for visual (blood blood BLOOD!!111)?
Dark Crusade and Soulstorm bring even more limits to more looks like tabletop Wh40k. Imperial Guard can have only guardsman squads mostly in SS. It was not for balance or make game be like small army tactics. They do that exactly to try keep it Wh40k. Well, DoW is too much skirmish\multiplayer game. All DoW1-2 singleplayer's try to be something 'in between' and all failed it. Too much large armies for be about small armies, too much small to be big fightin', with AI have doubled units anyway. DoW2 singleplayer are same. It was again too much small trying to show big battles and again AI opponent in campaign have separated doubled armies with separated unit limits.
Winter Assault are not big exception from it. They try show big conflict with small armies (for player).
this is such a terrible attempt at gaslighting lol. Winter assault is single handedly the most tedious and press x to win of any dawn of war campaigns. It's a huge waste of time and a slog to push yourself through. To the OP: ignore this gaslighter and winter assault and move on to dark crusade.