I’m really not sure why you’re taking this stance, but people have been calling large population servers (as is patently obvious by the term) Mega-servers for quite a while.
Conflating the term “Mega (very large) Server” with faction imbalance is somewhat understandable, I suppose, since most of the mega servers have become imbalanced.
However, if you’d like to clarify for yourself, you can look at historical usage of the term “Mega Server” on these forums and clearly see that it has been used to refer to large population servers, even while they were well balanced.
Here are some examples: