The land that can be used as "dense urban area" is strictly upper-bounded by zoning, precisely because it is so economically efficient: a few suburban homeowners cannot hope to compete financially with the ~400 potential high-rise condo owners vying to live on the same block, so instead they fight (and generally win) in the public-policy arena.

For the efficiency factor to overcome the desirability factor, we would have to actually issue the building permits to allow thriving urban areas to overtake some of their surrounding lower-density neighborhoods.

We've decided as a society that this is unacceptable, so urban areas will probably maintain their premium indefinitely. In a sense you're right. But only for self-inflicted public policy reasons.