An emphatic expression for 'if anything', 'especially', and 'it is', which shows that other alternatives are hardly conceivable.
Long explanation:
The grammar point Noun こそすれ is a conjunction which is used in written Japanese. It's an idiomatic representative of 'even if not anything else'. In a simpler definition, it means 'especially', or 'if anything'.The speaker is persistent on their statement and does not contemplate other alternatives.