That is what I am worried about. Stainless has about 15% the
conductivity of copper but I have seen outrageously expensive stainless
QFH antennas on some big outrageously expensive yachts that work great.

Long term, they might do better than copper, which wouldn't last as long.

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An antenna has both radiation and loss resistance.

Suppose a VHF copper dipole is 99% efficient.

If it is replaced with stainless steel which has 10 times the resistance
loss then the efficiency will fall to 90%.

Nobody will be able to detect any difference except that in 5 years time in
a marine environment the stainless steel dipole will still be working.

An understanding of ohms law is useful.