Can diversity be a political strength? If it can, what are some examples?
I don't think there is an easy answer to that question.
The strength of a group, political or otherwise, it's generally derived from unity. To be blunt, the simplest and surest path to unity in a group is to mobilize people into thinking that things are a matter of "Us vs them". "Them" being people having whatever characteristics are easiest to demonize. Another country, another ethnic group, another political group, etc.
We can see this effect, in the situation the United States has found itself in. The two primary political parties have mobilized their people against each other. This keeps the people in charge of each party strong, for the country as a whole very weak.