If the antenna system can be satisfactorily matched to the
transmitter
output impedance, it would seem to matter little whether the feed
line
currents are balanced, or, if they are not, by how much.

If there are no obvious common mode currents causing problems in the
shack, then of what consequence would an imbalance be, other than to
modify the radiation pattern, perhaps even beneficially?

Chuck, NT3G
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I agree with what you say.

But antenna (or line) unbalance and line-to-antenna impedance mismatch
are not entirely independent of each other.

An unbalanced line or antenna causes a small impedance mismatch.
Because it is small is the reason why it very often happens it doesn't
matter very much whether or not a balanced feedline is used.

For example, a coax line can be used quite successfully to feed a
balanced dipole.

And, in practice, no antenna is perfectly balanced about ground.
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Reg.