That would be true if it was just civilians fighting, but the military is usually on the side of the tyrant.

It’s mathematically better, I think that armed populace has a higher chance of revolt vs armed loyalist populace + armed military than unarmed populace vs unarmed loyalist + armed military.

And I also think the reasoning is that the anti-tyrannical populace will be much larger than the pro-tyrannical populace since if the tyrant has the support of the people then are they really a tyrant.