The isolator is required because the manufacturer specifies it.
They are not wrong. They require an isolator so you must fit one.
I realise you are too thick or belligerent to understand this.
The instructions and the regs must be used in conjunction with each other.
If the instructions are blatantly wrong, obviously you would use your judgement.
There is nothing WRONG with fitting a local isolator.
So if the regs DO NOT require one, yet the instructions DO, then you would have to fit one.
The regs are general guidance, they do not contain manufacturers instructions.