Cecil Moore wrote:

The myth is undoubtedly that the implied point of view is either popular
or developing.

From QRZ.com regarding tuners:

"The tuner has absolutely no effect at the antenna."

From eHam.net regarding tuners:

"Does nothing. The tuner as the other poster said,
just makes your radio happy."

The tuner doesn`t change the antenna specification, e.g. gain,
impedance, or pattern.
If you buy a beam antenna you will get this data, and the pattern of the
antenna is most time a free room pattern.

As the tuner is used to match the impedance of the radio to the line it
will effect the power getting to the antenna or the signal received from
the antenna if it is passed through the tuner.

--
DK
DJ4PB