Richard Harrison wrote:
. . .
If the antenna is operated off-resonance, it still works but with less
vigor due to diminished current opposed by inherent reactance.
. . .

This is true only if no effort has been made to match the antenna to the
transmitter. If it's matched, it will have the same current and "vigor"
as a resonant antenna. Assuming negligible loss, if 100 watts is applied
to resonant and non-resonant antennas by any means, 100 watts will be
radiated from each.

Roy Lewallen, W7EL