Er, the rule is right there in the Loremaster text and the meaning of the English words it uses. "As if" means you copy the thing referenced plus anything and everything based on it*. If a Wizard would gain 4 new spells but I only gain 2, then regardless of the reason for the difference it is most definitely true that I am not gaining new spells as if I were a Wizard. If I were gaining new spells as if I were a Wizard, I'd have the same number - 4.
* More formally, it means you construct a hypothetical while pretending that the "as if" clause is absolutely true in every regard, then copy the relevant parts of the hypothetical. Loremaster gains new spells "as if Wizard"? Level up a copy of your character in Wizard. Note the copy's spells known. You gain the spells noted.