Hmm, I'd say that on a 2018-era machine, you won't measure this in raw CPU throughput. In all probablity, your cores are fast enough to mask the context switching. The performance deficit here is strictly in the domain of motion-to-photon latency or frame pacing. I guess my point is that in xfce's split architecture, the compositor acts as just another X11 client.

This enforces a path where window contents often round-trip through the X server before composition. Quantitatively, this typically adds at least one frame of input lag compared to the zero-copy direct scanout path available to monolithic wayland compositors. You likely won't notice this while editing text. However, the architecture doesn't perform well when you attach an external monitor. Since X11 shares a single virtual coordinate space, it cannot synchronize VBLANK across two outputs with different refresh rates or clock domains.

ps: and please don't call your 2018 machine vintage, it makes my secondary thinkpads feel prehistoric :D