How is this unnecessarily informal?

Question

I was reading this particular answer, when I found something interesting and confusing to me. The answer stated:

If one had to insert a particle in [会社{かいしゃ}など２３０の会社] that made sense, that particle would be 「の」. It would, however, be slightly wordy because there will be another 「の」 coming soon in 「２３０の会社」. It would also make the sentence sound unnecessarily informal as well.

It makes sense to me that it is more wordy. However, I would have guessed the opposite for formality. I assumed that by adding the extra particle it would become more formal.

So, this claim that adding the particle is 'unnecessarily informal' is at odds with my understanding.

How is it unnecessarily informal?

Answer 1

Often a shorter version sounds stiffer or more literary/academic/technical.

• Masu-stem is stiffer than te-form to join clauses
• だ before ～と見なす, ～とする is usually not said in legal sentences

AなどB is another example. But the difference is small, and AなどのB is not particularly casual, either. An even stiffer variant is 等（とう）, which is a norm in legal sentences but should be avoided in ordinary business conversations. See: Inaccurate ruby for 等?

It's difficult to give a shared background for this, but in general, a highly stiff and literary material tends to have more (on-yomi) kanji and less kana.