Comment by derefr

Try using any of that 25-year-old software with accessibility devices, or at any DPI scaling other than 96x96, or split between two monitors with different refresh rates (or worse yet, two monitors connected to two different GPUs), or with sound or 3D accel that works over RDP, or with an RTL UI language. Those are some of the many "whats" that you get batteries-included in modern OS UI frameworks in exchange for the added overhead.