Not so strange considering 2 centuries seperate English colonialism in the Americas with Nelson Mandela. Bear in mind that the profits from Scottish trade with English colonies built the [first] New Town so it isn't so strange that streets would be named in deference to the monarchy of the time. It was also done as a means of consolodating the new notion of British Nationhood as well as affirming Glasgows loyalty to the Crown and normalising the new regime.
Nelson Mandela Place was named in a similar exercise of deference and as a means of expressing Glasgow's new found open-ness and cultural diversity - in a sense, another new notion of Nationhood.
I don't think it prudent nor right to sweep away parts of our history because it doesn't conform to present ideologies, smacks of sweeping things under the carpet to me.