There is quite obviously no mathematical error here as you claim. Not only do the verses not create an error, they don't specify anything enough for you to come to your conclusions as if they were undisputed.

As to your question, Islamic law uses what you call the "second attempt". And no, not only is it not clear from the verses that you are supposed to take their shares from the original amount, we have evidence that the shares were split into categories from the Sunnah. Four categories, first being fixed close kin, second being flexible kin, third being everyone else, fourth being anything specified in the will. If the inheritors all belong in the same category, we use a hierarchical method that has a predefined ratio. None of this violates the verses, which leaves enough room for all this.

What you did to these verses can be done to many others as well, if you don't know Arabic and use English (and making it seem as if the verse is clear on things it hasn't clarified upon), don't know the tafsir and don't know/don't consider the Sunnah or the narrations.

We don't use such a primitive way of distribution like you used in your example, which not only is incomplete, it's nonsensical since you didn't even split them into categories.

Of course, if you only take the Quran as your basis for law, it will be a problem, amongst many others that cannot be explained, and can be refuted by the practice of it recorded anyway.