No, of course not, as there are way more influences to that language (p.e. arabian is a substrate of spanish and portuguese (I guess), just like Germanic is a substrate of French etc.). What I was trying to say is that knowing the derivation of a word and believe me, there are many words, especially nouns (p.e. castle, from latin castellum --> spanish: castillo, french: château, italian: castello, portuguese: castelo) and verbs (to drink: latin: bibere, french: boire, spanish: beber, italian: bere, portuguese: beber) which show an analogy that comes from latin. I am not talking about the structure of the languages, of course there has been an evolution in any of them, but you can recognize many words from knowing the latin derivation.
Nevertheless I must agree that it is pretty easy to learn the romanistic languages when starting with one of them, just like you said, with italian language.