Yes, learning all the characters has a steep 
    learning curve, but once one passes that stage, ...

One never passes that stage, though? Even once you know the 6,000 characters that people often cite as being needed to read a novel, you'll still run into characters that you don't know (especially in proper names, but also in less common, especially literary or chengyu, vocabulary).

I also disagree about the "grammatical similarity", but at the point of fluency we're talking about here (day-to-day fluency in idiomatic Chinese), that doesn't matter anyway, not even a bit.