I agree with HillRider that even recent, mainstream Shimano hubs are all over the map for wrench sizes. In addition to the nominal flat sizing, some hubs are very picky about wrench thickness. I have encountered at least one hub where a full-size Park "pro" wrench couldn't fit in the space behind the locknut face (many of their hubs leave the locknut face round, probably to maximize contact area with the dropout, and just mill a narrow slot in behind it). As a result, I now also have a collection of the Park double-ended wrenches, which seem to be thinner and don't have the fancy anti-rust coating. They're also stubbier and so can't generate (or withstand) as much torque, I would imagine, but are fine for what they're used for.

So I would say you really can't have too many cone wrenches, but do switch up on brands and styles to maximize flexibility.