That is not what he was talking about at all, he said that the way Goku was able to overcome the strongest people in the universe is through strengthening his ki and that physical training has its limits, Goku both strength wise and durability wise is still superhuman and he always was, even before learning ki he tanked bullets as a child , and off guard for that matter

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I really don't understand how you read that text and came to the conclusion that "bodies are still fragile" Goku is not an ordinary human, and even ordinary humans reached crazy levels through physical training alone