Fair point.
The only "major" thing that happened was essentially a 15-year long standoff between Jin and Wu along the Yellow River, and that's pretty much it.
Doesn't exactly compare to the Yellow Turban Rebellion, Red Cliffs, Wuzhang Plains, Hefei, Hulao Gate, and Xiapi, now, does it? xD
Zhuge Dan at least had a character arc in 8(XL) that led to his rebellion (the game paints it as one result of Sima Shi dying and Sima Zhao being, well, Sima Zhao). And you could play as him in previous battles
Xiahou Ba is there as an NPC for a couple battles until the coup d'état happens (which is... maybe two battles total?), and then he's just gone, unless you unlock the hypothetical stage to get him back. I'd say nepotism of sorts is a good explanation for his inclusion.
Ah, true! I forgot about that one.