Actually, I will go out on a limb over this point.

I have always found that a mis-matched, or "out of specs", antenna will
continue to "ring the ether" a bit more efficiently than it will "pluck
a signal from the ether."

Concur.
RX level can be even more noticeable on high Q antennas off-resonance as you
would expect.

Now add the line loss. Also, reflections don't seem to matter much with CW
and SSB but can have an effect on some digital modes and certainly
television.

With solid state PAs, not all are created equal, and shutback often errs on
the side of keeping warranty costs down. Stability is in the reach of most
modern ones now. The current can be dealt with if you can get the heat out
of the junction to a point. But the voltage rise is the killer.

Also be aware that any transmission line will be significant in your
measurements at the rig end.

The MFJ can see anti-resonance if it doesn't get confused on other oddities
such as coax length or connector humps, reflections. It can get pretty
dicey when you sweep because all these things jump out at you when the load
is out of resonance and or mismatches anywhere on the line. Not to mention
the harmonics in the unit when you are looking at high impedances.