I don't quite know well in such matter. Displaying frame buffer is one complicated area in QEMU which I do not understand very well. It does seem to use synchronous update based on one-shot display timer. This implementation very much favors virtualization performance to keep the VMCPU busy without taking VMEXIT for display update until the timer expired. This can be observed with PCPBENCH that the insane FPS from QEMU does not even produce any tearing. On the other hand, there is noticeable screen tearing once the FPS exceeded the panel refresh rate with DOSBox. Some would call this as "optimization" but then it makes comparison "not quite fair" as DOSBox was paying the price of updating frame buffer and display it while QEMU was updating the frame buffer but only display it at specific intervals.
If you skipped frames, then benchmark timing loops will timed faster and then score would improve, I guess. I had seen inflated 3DMark2000 scores when my GL pass-through was mishandling some vertex calls and basically the calls would end up faster. Fortunately, there were rendering artifacts that was easily noticed. When those were fixed, 3DMark2000 scores tanked.
Modern display software architecture requires predictable V-SYNC. It is a waste in both power and bandwidth to produce more frames than can be displayed in time.