arXiv:2507.19918v4 Announce Type: replace Abstract: This paper presents a unified perspective based on Davis-Wielandt (DW) shell of linear subspaces for graphical stability analysis of multi-input and multi-output linear time-invariant feedback systems. Connections between DW shells and various graphical representations, as well as gain and phase measures, are established through an intuitive geometric perspective. We establish a strict DW separation theorem which characterizes subspace separation and provides a basis for comparing the implications and relative conservatism of graphical separation conditions. In particular, we introduce the rotated scaled relative graph ($\theta$-SRG) and show that its separation is equivalent to DW shell separation and is therefore the least conservative among all the graphical conditions considered. We derive pointwise and boundary stability conditions for bi-component feedback interconnections and establish a weak DW separation result that relaxes the strict separation requirement at open-loop poles. We also discuss applications to robust stability analysis and provide a numerical example illustrating how DW shells serve as a more reliable robustness indicator.