Once again, the only signal you will ever transmit is the signal at the same frequency that you're feeding through the wire. The antenna is only there to maximize the signal strength.

If you feed a 1cm wavelength signal through a 10m antenna you will still get a 1cm signal on the air. The problem is that the strength of that signal will be extremely poor.

Lastly, you can indeed replace the monopole antenna for a wire. The benefit of the antenna is that it can stay straight, otherwise it is indeed just a glorified wire.