I agree for the most part. Fact is that the Bijuu do not belong to Nagato, they're a seperate power that needs to be sealed inside Gedo Mazo. If we look at it chronological then yes, Nagato can use Gedo Mazo with seven Bijuu inside it - but then again, if we go by that, Nagato can only use that kind of Gedo Mazo while being crippled, since he didn't possess any Bijuu while being healthy.
So, from the chronological point of view it's either a crippled Nagato with a powered Gedo Mazo or a healthy Nagato with an unpowered Gedo Mazo.
So, in a fair fight, Nagato needs to be impaled by the Chakra rods if he wants Gedo Mazo to use the soul dragon or any Chakra based attack. It can use 'Taijutsu' without impaling him, of course, but did you see how small Gedo Mazo was when Nagato summoned it? Kishi is sometimes pretty sloppy when it comes to size-relations, but this cannot be a coincidence. Whereas now one of Gedo Mazo's fingers is bigger than a human, against Hanzo its entire hand was hardly twice as big as Nagato, making it considerably smaller. That's most likely due to the lack of Chakra; Kyuubi also shrunk drastically after Minato had sealed one half of its Chakra. Well, but that's just my guess. Maybe it was just sloppy drawn by Kishi.