With due respect, the case law quoted above pertains to inverted duty structure which has no relevance with the query asked about refund on export of goods (i.e. zero rated supply).
As far as refund of input services is concerned, pls note that the Rule 89 itself is very clear in this regard. Rule 89(4) reads as under:
(4) In the case of zero-rated supply of goods or services or both without payment of tax under bond or letter of undertaking in accordance with the provisions of sub-section (3) of section 16 of the Integrated Goods and Services Tax Act, 2017 (13 of 2017), refund of input tax credit shall be granted as per the following formula –
Refund Amount = (Turnover of zero-rated supply of goods + Turnover of zero-rated supply of services) x Net ITC ÷Adjusted Total Turnover
Where, -
(A) "Refund amount" means the maximum refund that is admissible;
(B) "Net ITC" means input tax credit availed on inputs and input services during the relevant period ;
(C) “Turnover of zero-rated supply of goods" means the value of zero-rated supply of goods made during the relevant period without payment of tax under bond or letter of undertaking or the value which is 1.5 times the value of like goods domestically supplied by the same or, similarly placed, supplier, as declared by the supplier, whichever is less;
(D) "Turnover of zero-rated supply of services" means the value of zero-rated supply of services made without payment of tax under bond or letter of undertaking, calculated in the following manner, namely:-
Zero-rated supply of services is the aggregate of the payments received during the relevant period for zero-rated supply of services and zero-rated supply of services where supply has been completed for which payment had been received in advance in any period prior to the relevant period reduced by advances received for zero-rated supply of services for which the supply of services has not been completed during the relevant period;
(E) “Adjusted Total Turnover” means the sum total of the value of-
(a) the turnover in a State or a Union territory, as defined under clause (112) of section 2, excluding the turnover of services; and
(b) the turnover of zero-rated supply of services determined in terms of clause (D) above and non-zero-rated supply of services,
excluding the value of exempt supplies other than zero rated supplies during the relevant period
(F) “Relevant period” means the period for which the claim has been filed.
Explanation. – For the purposes of this sub-rule, the value of goods exported out of India shall be taken as –
(i) the Free on Board (FOB) value declared in the Shipping Bill or Bill of Export form, as the case may be, as per the Shipping Bill and Bill of Export (Forms) Regulations, 2017; or
(ii) the value declared in tax invoice or bill of supply,
whichever is less.
According to section 2(60) of the Act, “input service” means any service used or intended to be used by a supplier in the course or furtherance of business;
Since the Rules are crystal clear in this regard, you may bring these relevant provisions to the attention of the Proper Officer.