Translation:I like Chemistry more than Geography.
I agree, I think that 'I like chemistry better than geography' should be accepted as a translation for this too
You could say Η Χημεία μου αρέσει καλύτερα από την Γεωγραφία which matches 'better' and it would still be a correct phrase in Greek, but actually this is not as common as using περισσότερο, which of course means 'more'. Therefore it may be best to keep the current translation.
'better than' here seems to be an idiom in English (Shakespeare perhaps)since 'I like it well' seems a bit archaic (, but 'I like this better than that' or 'I like it well enough' are fully normal and contemporary. So I think it should be accepted as a translation from the Greek to English (but not the other way around).
In greek, (i don't know if that also applies in english) sciences are capitalized.