Whole-genome duplication (WGD) has been proposed as a catalyst for evolutionary innovation in seed plants and angiosperms, yet their occurrence remains contentious. By integrating gene dosage balance principles with phylogenomic reconciliation and probabilistic modeling, we revisit the debated ancestral seed and angiosperm WGDs. Leveraging dosage-sensitive orthologous gene groups (OGs) as evolutionary markers across representative plants for gene tree/species tree reconciliation, we demonstrate that gene retention patterns in Amborella and Aristolochia—early-diverging plants lacking post–angiosperm origin WGDs—reveal a single gene duplication peak predating the seed plant diversification, with no signal of ancestral angiosperm WGD. Correlation analyses of observed and expected OG copy numbers, given proposed WGD(s), further refute an angiosperm WGD. Probabilistic retention modeling analysis corroborates these findings and shows that retention rates of dosage-sensitive genes from the putative angiosperm WGD are extremely low. Besides, our study establishes that genes inferred to have higher dosage sensitivity based on their sequential retention following WGD events may have increased utility in resolving ancestral polyploidy.