I tend to agree with you. If the machine has it's own protection, the upstream protection could be anything.
As far as Voltage Drop the larger (1/0) conductors are a plus.
The J box and splice sounds like the best way to accomplish this so that is not a problem.
Now, even though you and I agree, it doesn't hold much weight, the manufacturer has found this neccessry for some valid reason and to maintain warranty and or safety (more important) they say you must do it.
Roger
