> Objective history book would be ... decisions and... bias

No, not necessarily. From the events you go to the chains of events, the clusters, the trends, the teachings etc.

Similarly to experimental science, where you go from the protocols ("this happened there then") to the "laws".

The role of «decisions and bias» could be limited, with some similar quantitative, and maybe collaborative (aggregation of multi-agent contribution) approach that ranked the outputs through a computed importance.

Even a timeline would be subjective as the author would have to chose what to include.

youve completely lost sight of the forest. there are little granules of subjectivity like the ones you nitpick about and there are huge boulders of subjective nonsense that leave you with a giant bump on your head -- the kind that are caused by dogma like race/gender politics, religion, war etc. the absence of these is what is desperately needed. to wave away the boulders because of the granules is idiotic. ive read books that looked at war objectively, excised moral dogma from religion and omitted race/gender crusading entirely and its very good.