In addition to Ron's answer:
So far, I only thought of these potential problems:
the CRC may fail often when the frame is too big
big frames could be less flexible regarding flow control
Absolutely. In addition, larger frames can cause more latency/jitter in spite of QoS - larger frames means less granular traffic.
Since frames are handled by hardware, ...
We've had jumbo frames for decades.
One reason they're not in common use on the Internet is IPv4 (and later IPv6) overlooked any possibility of having underlying layer-2 networks with connected nodes having different MTUs (or MRUs.)
ARP and ICMP do not have the ability to allow nodes to negotiate a mutually-agreeable MTU/MRU.
So for example, Internet ...
You’re missing the biggest problem: billions of dollars of equipment would need to be replaced, and essentially all at once. Who would pay that for just a modest increase in efficiency?
In your previous example, you'd save the 14 bytes per Ethernet frame, or less than 1% of the total transmission size. Sounds like a hard sell to me.
You explained that you're creating a physical network diagram and that often means the location of devices and the cables interconnecting them. Any other use of physical network diagram is going to be confusing.
You'll want more than one diagram to help you plan and communicate your design to other stakeholders. A diagram of rack/room/conduit locations is ...