Midtown is the best place for Class B FMs and TV to reach the full market with OTA signals. Nearly 2/3 of the market is not Manhattan and the Boroughs.
To TV the location is a bit less important than the cost... since so much NY HDA viewing is via cable or satellite distribution and not OTA. For FMs, the ESB is by far the best.
Look at WPAT, which was willing to take a power cut to stay at the ESB (due to spacing) rather than going back to the location that they had pre-9/11. That's because they prefer the Midtown location for coverage.
Building a 1500' tower in the "outskirts" is not going to happen as anything that would cover the market well won't get FAA clearance, zoning and permits (think NIMBY) and finding affordable, near-in land is likely not available.
I believe that only one FM that could be on the ESB is not... WBAI. And that is due to the WBAI inability to pay the rent at the ESB. Many if not most of the ESB FMs have backups at the Condé-Nast location, also in Midtown.