Romance of the Three Kingdoms is based on the Record of the Three Kingdoms by Zhou Yu. The latter is a historical record. In addition Sima Quan also recorded the events. The "Romance" is basically a novelization, meaning "romanticization" on actual events. The ROTK is actually written in the 14th Century during the Ming Dynasty, more than a millennia after the TK occurred.
As such the original printed text of the novel had illustrations of the characters wearing what is basically Ming vintage armor and Ming vintage weapons. For example the Guan Dao, the weapon which Guan Yu is most famous for, could not have been possibly been invented in the TK period, although such pole arm Daos are common among the elite forces of the Ming army.
Actual TK warfare should have been more like the late Han period, with main troops carrying halberd or "ge", with crossbow troops. Cavalry would be predominant with Cao Cao's forces, the Wei, since the Wei controls the northern borders and have access in recruiting northern nomadic horsemen, plus the grasslands could sustain growth and nurturing of large cavalry armies. The one difference in the TK period over the late Han period is the use of the stirrup, which allowed the use of heavier armored cavalry with melee weapons, basically a spear, basically horse mounted shock troops, aka knights.
What I find very interesting in the battle of Red Cliffs is the Wu's use of amphibious troops or commandos, meaning marines, along with amphibious assault vessels, to set Cao Cao's invasion fleet on fire. The marines were picked and trained to counter sea sickness and to fight in the decks of ships.
the armours and weapons use during TK are identical to Chin's terra cotta warriors and smaller's terra cotta warriors from the han's dynasty,
