Complex sentence: But, his details are brief and mostly just list rulers without referring to their real names rather than going on about deeds that each one did during their reign, which keeps in line with Al-Biruni's mission to try to stay away from political histories.
Split into simpler sentences: But, his details are brief and mostly just list rulers without referring to their real names. He did not go on about deeds that each one carried out during their reign, which keeps in line with Al-Biruni's mission to try to stay away from political histories.