I'm not sure this is really a historical question; The Romance of the Three Kingdoms (三國演義, "Three Kingdoms Historical Novel") is a novel and not actually the work of a historian. It was written more than a thousand years after the events described, and very much reflects the outlook of its time rather than an analysis of the actual war. That is, the story and characters were framed from an early Ming dynasty perspective rather than reflecting Han-dynasty or contemporary views and interpretations, and definitely sacrificing historical accuracy in order to do so.

In the novel, Liu Bei, and by extension the kingdom he founded, are presented very much as the inheritor and torch-bearer of Han morality, bravely opposed to the cynical scheming and power-grabbing of Cao Cao and Sun Quan, though the latter gets a lot less attention.

The fictional Liu Bei is basically a paragon of Confucian values, governing his kingdom (he is also appropriately reluctant to take on the mantle of king) in a properly Confucian moralistic manner, surrounded by a coterie of similarly morally upright warriors (e.g. Guan Yu) and ministers (e.g. Zhuge Liang) all of whom fit neatly into Confucian archetypes. Many of them are in fact seen as such perfect exemplars of these roles that they have been deified (or semi-deified, it's complicated) and are revered in modern Chinese religion. The text lays this theme on pretty thick in places, really.

So, in short, Liu Bei in the Three Kingdoms isn't the historical Liu Bei, and doesn't present much of a mystery or challenge to interpretation in his fictional form either.