Splitting off AWS wouldn't be enough on its own, but I think the argument would be that Amazon makes a substantial amount of its operating income from AWS (70% in the latest quarter: https://ir.aboutamazon.com/news-release/news-release-details...), which allows it to fund anti-competitive marketplace practices like undercutting competitors at a loss to force them out of business. It would be more difficult to sustain such practices without AWS income.