Hi Tanit
"Grammatically correct" does not automatically mean that a usage will sound "natural" -- especially in informal English. This is especially true in sentences such as "It's me" or "That's him" or "He's taller than her". All of those sentences sound completely natural, but might be criticized as being "incorrect" or "overly informal" in a formal context.
You gave a very good example of how a sentence can become ambiguous when too much is omitted:
(a) I love her more than you.Does that mean "
I love her more than you love her"?
Or does that mean "
I love her more than I love you"?
Sentence (a) is ambiguous because the word 'you' can be used as either an object or a subject. However, the next sentence should not be at all ambiguous:
(b) I love her more than him.Technically speaking, sentence (b) can
only mean "
I love her more than I love him".
In informal English, however, it's possible that you might hear sentence (b) used to mean "I love her more than he loves her".
It would not surprise me at all to hear someone say "I have more money than him." Technically speaking, that is a grammatically incorrect sentence, but I don't think the meaning of that particular sentence is ambiguous. People would only understand that last sentence to mean "I have more money than he does." People would automatically reject a possible meaning of "I have more money than I have him" since that doesn't make any sense.
Does that answer your question?