It looks like MTU isn't mentioned because the author is looking for the minimum possible packet for port scanning

I'm told modern gigabit ethernet devices derive practically no benefit from jumbo frames, and the pitfalls of using them are legion.

Each frame is a CPU-hogging interrupt so if your bottleneck is the CPU, then jumbo frames will help by moving more data for the same number of frames. This happens easily on routers with low-power CPU.

This is only true for very basic Ethernet hardware. Various interrupt mitigation schemes came along in the late 90s along with gigabit ethernet. Even low-end Realtek gigabit chips have various segmentation offload and interrupt coalescing features these days.

Those schemes have varying levels of effectiveness. I personally experienced this wasn't a given even as late as the 2005-2010 era, when our purchases were shifted towards certain models specifically due to the issues with drivers or buffer limits.

I learned never to underestimate how much functionality a major vendor will be willing to cut if it saves $.10 per unit shipped…