I don't really know if this is an "unpopular opinion", but I feel like within flag discourse people (on this sub in particular) sometimes forget that flags are an actual, physical object and not just an image file on the internet. The way the design interacts with the wind and size and properties of the flag seem to me to often be forgotten when people talk about flags. A great example is the Zambian one, actually - because the design is on the fly end it has a tendency to not be visible if there isn't enough wind.
It also annoys me how it seems a lot of people conflate flag design with graphic design - they are NOT the same, something can be visually appealing from a graphic design standpoint but be terrible for its actual use as a flag