During the development of the MSC platform at ENSO Origins, the initial plan was to build a traditional Single-Page Application (SPA) using plain React. However, as requirements evolved, we migrated to Next.js 16 (App Router). This shift solved several concrete problems. First, it eliminated the typical visual flicker of SPAs by using native middleware (`middleware.ts`) to validate JWT tokens on the server and apply Role-Based Access Control (RBAC) before any rendering occurred. Second, the App Router enabled persistent nested layouts, keeping the navigation bar and side menus in memory during dashboard transitions. Finally, adopting React Server Components (RSC) allowed us to fetch profile data and schedule lists directly on the server, significantly reducing the client bundle size and hiding API endpoints from the browser.