This chapter addresses the paradox of why structurally diverse parties exhibit a shared “functional convergence”. Shifting the analytical focus from variance to direction, it documents the Europe-wide rise of disintermediation: the systematic hollowing out of the intermediate bureaucratic layers that traditionally connected leadership to the base. Through the Party Disintermediation Index, the analysis reveals a consistent upward trend across eleven democracies, identifying the emergence of the “Curvilinear Party”, an organization characterized by a powerful leadership and an atomized membership, but an empty core. The chapter decomposes this trend into three mechanisms: the “financial short-circuit” of state funding, the flattening of hierarchical structures, and the adoption of “open door” representative strategies like direct primaries. Case studies of the British Labour Party and the Italian Democratic Party illustrate how democratization reforms often serve as vehicles for leader-centric centralization. The findings suggest that European parties are transforming into plebiscitary machines, replacing the stabilizing logic of delegation with a volatile direct mandate that prioritizes short-term responsiveness over long-term integration.