The only metal that can be used on both parts of a sliding or rotating metal to metal bearing is cast iron
The zinc on zinc is fine if the bike is used at least on day a week.
When they were designed tthe bikes were daily transport.
The zinc oxadizes and the zinc oxide is quite porous and adsorbs some fuel vapour which keeps it lubricated.
Only when they sit unused for months and over cleaned that the slides stick.
Just about all of the leaded copper base alloys are fine running against each other.