I wholeheartedly disagree. The difference is in the lore. The personality of the Legion is arguably lacking, but that's the point. They're there to do a job and get paid mainly. This isn't their land, though some of them are Nords. Tullius however embodies this very well. He seems tired, weary, and ready to leave. Uncaring for the locals there.
The Stormcloaks are angry, and proud nationalists. They're harsh to those that don't support the cause, but treat those that do as brothers. Listen to Ulfric Stormcloak's speech, or listen to him talk about the war. He's chuck full of personality, and very charismatic. Galmar's the gruff guard dog, old grizzled warrior. Their soldiers are passionate because they're fighting for their land and its future. The civil war will decide the fate of all Nords of Skyrim, and possibly even the Empire, if the Stormcloaks win, since their only province in the Empire would be High Rock, separated from Cyrodiil by two provinces. Which means its unlikely that they'd stay, and Cyrodiil would be a Kingdom once more.