because that was just a bit of his chakra.
now, the maths you wanted to prove you wrong:
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this shows the Shinju as about 3x higher than the clouds, making it between 21,000 and 66,000 feet high. Where naruto cut the god tree it was about 1/6 the height of the tree, so for simplicity, 3500 feet, or slightly over a kilometre.
from this and you saying that dead hagoromo is only 1/10,000,000 of alive hagoromo, and the fact that naruto only has half of hagoromos power, we can see that hagoromo could, without difficulty, shoot death beams that are over 20 million kilometres long.
the earth, is about 12,000 kilometres. this puts hagoromo not so much in Dbz levels, but in those obscure mangas where universes are more or less putty.(some over-exaduration, as thats smaller than the solar system but you get the idea)
now, as hagoromo hasn't yet blown up anything larger than a grain of dust, we see that maths and manga go together like people who are bad at metaphors and this thread.
#Math'd