Sure, those other metals have a higher oxidation potential than iron, but that's why they're normally found in the oxidised state. Most of them are capable of stripping oxygen from CO2 if they exist as reduced metals.

The trick is, a biological system would need something like that available to dump the oxygen onto from the iron so that the nett reaction is downhill. (Many organic compounds can also function as energetic oxygen acceptors). Those metals aren't just going to be sitting around waiting to be used. they'll have oxidised long ago.

So if we find chemical systems on Mars (or other planets) that are out of balance to the extent of having strong reducing or oxidising agents, then it's a hint that something biological is pumping the chemistry.

On Earth, the oxygen in the atmosphere is just such a sign. Photosynthesis is a very interesting reaction.

On Mars, the oxidising effect of the regolith was at first taken as a sign of biochemistry, but later explained as inorganic peroxides generated by UV irradiation.