The information below is extracted from the "benchmark" 1937 I.R.E. paper* of Brown, Lewis & Epstein of RCA Laboratories, and is based on their accurately measured data for these systems.
IMO, the outlined and underlined text at the bottom of this clip is worth remembering, and deserves greater access/acceptance.
*Proceedings of the Institute of Radio ...
Below is a graphic comparing some of the operational parameters of ground-mounted and elevated vertical radiators for the 40-meter band.
Their performance when installed at sites with relatively poor Earth conductivity is fairly similar.