Li- and Mn-rich layered oxides (LMR) have attracted significant research interest because of their potential merits of low cost and high capacity that exceed current Ni-rich cathodes. Despite nearly two decades of intensive investigations, however, the structural nature of LMRs, particularly with respect to Li₂MnO₃-like domains has remained under debate. Early structure models described LMRs as an intergrowth of monoclinic Li₂MnO₃ (C2/m) and rhombohedral LiTMO₂ (R3̅m) phases. In contrast, subsequent studies revealed that these structural signatures can also arise from local Li–Mn ordering within a single solid-solution framework. These conflicting interpretations have complicated a clear understanding of structure-property relationships and impeded progress toward the commercial implementation of LMRs. In this perspective, we present a unified view showing that the structural state of LMRs is determined not solely by bulk composition but critically by synthesis conditions. By integrating evidence related to precursor chemistry and calcination parameters, we elaborate on how cation homogeneity, the distribution of excess Li, Mn oxidation states, and diffusion kinetics collectively dictate whether Li₂MnO₃ forms extended slabs or nanoscale, delocalized structural motifs. Through a comparative assessment of synthesis routes, we review how LMRs span a continuous structural spectrum rather than conforming to a simple binary phase model. Finally, we outline synthesis-driven design principles for controlling the evolution of Li₂MnO₃ domains, providing practical guidelines to develop structurally robust, high-energy LMR cathodes.