The light skin assumption was partly a product of a broader prior in early ancient genomics research. When the 2012 genome was analyzed, the methods for inferring pigmentation from ancient DNA were less developed, and the implicit assumption that an Alpine European from several thousand years ago would have had the skin tone of a modern southern European was not unreasonable given what was known then. The genomic research that has accumulated since 2012 has repeatedly shown that ancient Europeans — hunter-gatherers and early farmers alike — typically had darker skin than modern Europeans, apparently due to lighter pigmentation being under positive selection in post-Neolithic European populations over the past several thousand years. Ötzi fits this pattern: an ancient European with darker pigmentation than would be predicted from modern comparisons.
The hair assumption was more directly an artifact of the contaminated genome, combined with a default to a “typical” middle-aged man appearance. The 2012 genome, with its contamination and lower coverage, did not reveal the baldness-associated alleles that the 2023 genome found clearly. The Kennis reconstruction gave Ötzi a full head of hair because there was no genomic reason to do otherwise, and the sparse hair found with the mummy could be explained by taphonomy.
The steppe ancestry assumption was the most directly a product of the contamination problem. It produced an anachronistic result — steppe ancestry before the steppe expansion — that should have been treated with more skepticism but was instead discussed and sometimes reported as a genuine finding.
The 2023 reanalysis could not have been done without the decade of methodological development that intervened between the two studies. Higher coverage, lower contamination, and a vastly larger comparison dataset of ancient European genomes all contributed to the new picture.