I think it might be ok to say going to the front plate is wrong.
It not only OK to say, but is 100% correct & no more evidence is needed.
Total understanding of grounding or earthing is the only important consideration in this & other ground situations.
Connecting this braided strap to the engine plate does not
complete the ground circuit.
The engine mounts are called insulators for good reason they insulate the frame & engine not only for vibration etc. but also will stop electrical circuit flow.
The strap is meant to ensure the engine & it's major electrical components are grounded to the vehicle frame
by a substantial strap/ground. This is accomplished by locating the end of the braided strap on the frame side of the engine mount. Then the frame is securely grounded by the earth lead to the battery. Voila....a completed ground circuit capable of carrying sufficient current.
Connecting the strap in question's end to any engine location & not the frame will contribute to hard/laboured starter operation. Something we hear of so often on G503 6V systems.
As an aside I recommend a small modification to the ground circuit to alleviate any issues here, by having 'a looped' good heavy ground across from a frame side engine mount bolt to the engine side of the engine mounting stud thus eliminating the insulator issue.