All i did was skim the OP and look at last line. So, i'll show you the error of your ways.
First of all, you used the scan of 7 combined bijuu dama's to estimate the size of naruto's own. But, at least you stated naruto's own could be roughly 1/2 the size. Now, this is unlikely, though naruto made a ball of similar size( off a Flash TBB for some weird reason), his bijuu-dama should be 1/7 the area of that scan. In any case, just for argument sake, I'll show you what half that explosion would look like. It's completely and utterly smaller. What you must not forget is that, 1/2 of that cicle is actually 1/4 the circumferance and a whole lot less the Area.
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In other words, Take away hashi's mokuton and goju rashoumon still deflects the tbb which would cause said explosion.
EDIT: Browsed some replies and understood point of thread a little more. Either way, Naruto's tbb would cover at most 1/4 of the circumference of that circle and should have 1/7th the total Power.