I have a more nuanced perspective. Most of the time, what we think of as a “city” is actually two real-world features: a human settlement and an administrative area that happen to share the same name. So of course there would be two elements in OSM. For convenience, laypeople often think of them as one and the same, and in some countries, they might be coextensive. But these are regional assumptions that really break down in some countries (starts around 15:30), not something we can base a global tagging scheme on.
For context, I’m coming from a country where settlements spread organically, usually with minimal planning, and administrative areas often try to approximate these development patterns until they give up, sometimes with spectacular results. When someone wants to go to Atlanta, they don’t particularly care about the outskirts; better to take them to the city center – specifically, the Five Points intersection, the origin point of the city’s street grid.
Meanwhile, any renderer that sizes city labels by population needs to consider the full population of the Atlanta urban area, not only the administrative City of Atlanta but also giant but obscure suburbs like Sandy Springs. In fact, more than half of Atlanta’s urban population lives outside any local administrative boundary, in unincorporated areas such as what the Census calls “Northeast Cobb CCD” for statistical purposes. (We don’t map any of these purely statistical areas, which would resemble cadastral mapping at high zoom levels.) Ideally, the Atlanta boundary relation would have population=498715 while the Atlanta place point would have population=5100112 – a different order of magnitude.
Incidentally, the administrative area’s name doesn’t necessarily match the settlement’s, even if they are very closely related. In New York, two adjacent settlements can be peers and share the same name, but their administrative areas have different designations and thus different name=* tags. I understand this is also the case in other regions with English influence. But plenty of other countries make a similar distinction between the settlement and the boundary. In fact, in China, the lowest-level administrative area is so often so much larger than the main population center that the local community had to be talked down from redefining population=*.