「AのほうがBより(property)」 vs. 「AはBより(property)」


In Genki I, chapter 10 I've learned:

> AのほうがBより(property)。 A is more (property) than B.
>
> Example: 中国のほうが日本より大きいです。

Now I just came across the following example sentence:

> 新かん線はふつうの電車より速いです。 The Shinkansen is faster than a normal train.

Which makes it seem to me that it is also valid to say:

> AはBより(property)。A is more (property) than B.
>
> Example: 中国は日本より大きいです。

My interpretation is that のほうが just means "the way of..." and is not really
needed or related to making comparisons.

Is this correct and if so, why does Genki teach comparisons with のほうが instead
of the more simple way with just the は particle?

EDIT: I think it's not a duplicate as suggested because this is mainly about
the role of the 「のほうが」 part.




I'm not a Japanese education expert so I can only guess, but certainly I can
point out some advantages of teaching AのほうがBより construction for comparison.

  1. **Modularity**

As you may already know, Japanese doesn't have the comparative form of
adjective. Thus if you want to express that in English, you have to get help
from other pieces of word. If you have learned comparison in AのほうがBより pattern,
you're also able to extract sub-expressions only containing either A or B.

> 中国のほうが日本より大きいです。 _China is larger than Japan._  
>  日本より大きいです。 _(It is) larger than Japan._  
>  中国のほうが大きいです。 _China is larger._  
>  cf. 中国は大きいです。 _China is **large**._

  2. **Topic neutrality**

The English sentence "A is more X than B" can be used whenever you want to
tell the fact. However, AはBよりX is not so much in this form, because it
involves topic management required by Japanese grammar.

> アメリカはカナダより大きいですか。 _Is US larger than Canada?_
>
> × カナダはアメリカより大きいです。  
>  ○ カナダがアメリカより大きいです。 _It is Canada that is larger than US._  
>  ○ カナダのほうがアメリカより大きいです。  
>  ○ アメリカはカナダほど大きくありません。 _US is not as large as Canada._

Providing they have never mentioned Canada in previous conversation and are
not going to, the first response turns very unnatural. If a learner was taught
in this pattern and reproduce it without thinking, they might end up uttering
ungrammatical sentence occasionally (and as you may know too, when to use は is
a big headache to learners from most part of the world). On this point, Aのほうが
is more safer option with presumably less frowns.

* * *

Further reading: [比較表現「A は B より～」再考
－日本語教育における的確な導入例を考える－](https://www.lang.nagoya-u.ac.jp/nichigen/menu7_folder/symposium/pdf/7/10.pdf)

