Dear Shri KALLESHAMURTHY MURTHY Ji,
Thanks for taking efforts to explain 'proportionate reversal of ITC' by quoting some legal provisions under GST and trying to provide some cogent 'legal reasoning' for the view taken by you.
Such efforts indeed help us to understand your legal reasoning better for taking a particular view, give our views thereon and make this 'discussion' lively, comprehensive & really meaningful for other contributors, visitors and querist/s.
Unfortunately but with due respect for your views, I beg to differ with your legal reasoning for following reasons:
A. Everyone agrees that GST is indeed payable by the taxpayer while selling subject goods at its 'scrap value'. In other words, said goods were sold in the course or furtherance of business of the taxpayer and thereby, falls within the term 'supply' u/s 7 of the CGST Act, 2017.
B. Consequently, it becomes clear that subject goods were used by the taxpayer in the course or furtherance of his business and thereby, he becomes eligible for credit of input tax charged on subject supply of goods or services or both to him u/s 16(1) of the CGST Act, 2017.
C. As subject goods were used only for 'business' (as defined u/s 2(17) of the CGST Act, 2017) of the taxpayer & there was no other purpose, Section 17(1) does not apply.
C1. Assuming that Section 17(1) indeed applies to given situation (though I disagree with such a proposition), even then, tax-payer needs to reverse only 5% of the ITC and not "proportionately" (i.e. 75%) in given situation (Reference: Rule 42(1)(j) of the CGST Rules, 2017).
D. When ITC is availed as per provisions of law and when same is NOT required to reverse (even "proportionately") as per provisions of law (as no-one could point out such provisions exists under GST law requiring "proportionate" ITC reversal in given situation), then, there is no legal question of 'enrichment of ITC' to the taxpayer.
These are ex facie views of mine and the same should not be construed as professional advice / suggestion or recommendation.