Those are a bit different.

is é mo thuairim go… uses é because the pronoun here refers not to the noun but to the go-subordinate phrase that follows, the copular structure is literally “my opinion (subject) is it (subpredicate): that XYZ (predicate)”. The é is subpredicate referring to go…, and clauses of this kind are always referred to with the default pronoun é, never í.

I’d expect í in cases like is í mo thuairim-se an tuairim gur aontaigh gach éinne léi (though even in such cases, I guess, is é mo thuairim would be common under influence of the type above).

I deal with this type here in my Guide to Irish “to be”.

is é an áit is different yet because áit is commonly referred to with masculine pronouns in general.

EDIT: and coincidentally, you’ll often get cad é before feminine stuff because cad é etymologically comes from caide, caidhe (< Old Irish cote) which was independent of gender of the following stuff, but was in early modern language reanalyzed as cad + pronoun and a new form cad í appeared, but the older cad é / caidé, goidé surviving in all contexts too.