Usage of 断然 as の-adjective?

Question

今年の欧州マイル路線では古馬や牡馬を交えても断然のＮＯ・１
At this year's European Mile route, even with other types of horses participating, (アルファセントーリ) is the absolute number one

I know that 断然 is a taru adjective so shouldn't it be 断然たるＮＯ・１ instead? Is 断然 a noun or an adjective here? if it's an adjectives, can I use other taru adjective with の instead of たる, like if they were の-adjectives? (I guess to not sound very strict/archaic)

Other sentences I found:

1. 現時点で断然の１番人気になりそうなのはアイルランドの３歳牝馬アルファセントーリです。

2. 全点に撥水加工を施したemuは、他ブランドに比べても断然の撥水性を保っています！

3. 私はずいぶん昔にBBTの単科科目を履修したことがあるのですが、その時に比べても断然のパワーアップ！！

Answer 1

Personally, I use it only as a standalone adverb meaning "by a huge margin" or "definitely (better)" when comparing things. That is to say, I usually use it with 方が/より, and I almost never attach の/な/に to 断然.

Regarding its no-/na-adjectival usage, I can find a few examples on BCCWJ, so it may not be entirely incorrect. But the number is very small as compared to its adverbial usage (i.e., no の/な/に at all), and I personally wouldn't recommend it.

• ダイビングやシュノーケルなら、バリより断然に沖縄の離島が最高にきれいですよ。
• 愛用してると以前に比べると疲れ具合が断然に違ってきます。
• 私の馬券は断然の1番人気のカワカミプリンセスからでしたが、…

As a taru-adjective, 断然たる(態度, 意志, etc) usually means "resolute", "determined" or "firm". 断然(と) means "determinedly", etc. (e.g., 政府に対して断然(と/たる/φ)抵抗を続ける) This meaning is fine in serious novels, but is too stiff, literary or outdated for a daily usage. 断然たる撥水性 sounds too grandiose and even a little funny to me.

Answer 2

Your question made me curious so I looked it up on a few different Japanese online dictionaries. 断然 has two different forms, the adjective (形容動詞) form and the adverb (副詞) form. The meanings depend on the form.

The adjective form, the と or たる form, refers to one's attitude of being uncompromising in the face of strong opposition.

The adverb form refers to being on a completely different level compared to others. You can use の(断然の1番) or な(断然な1番) with it, or just have no particle at all, i.e.「ほかの店より断然美味しい」.

So in your example, 断然の1番 refers to being "number 1 by far" and is being used in its adverbial form.