Further "で as 動作を行うときの様態 vs で as だ" clarifications

Question

asked this a while back: で as 動作を行うときの様態 vs で as だ. But i don't feel this aspect has ever become intuitive at all, especially for adjectives.

eg.

爽やかで抜けるような青空と、この香りとは対照的に、大きくせり出した柵のグレーが強い拒絶を示している。

(speaker in a prison by the ocean) The gray of the large jutting fence shows a strong rejection in contrast to the "爽やかで抜けるような(invigorating, like it was escaping)" sky and ocean scent.

結果は今ひとつでナンパにも技術が必要だと身にしみた

In the end I have come to realize "今ひとつで(i am lacking?)", even nanpa requires considerable skill.

i lean towards で as だ for both of these, but it's an very disjunctive read and very hard to naturally translate.

When does someone purposely choose to use this sort of sentence structure?

Answer 1

In both of your examples, で is not a particle but the te-form of the copula だ.

爽やかで抜けるような青空

Here, で is used to join na-adjectives (e.g., 簡単で便利な "easy and handy"). 爽やかな and 抜けるような both modify 青空. Note that the adverbial form of a na-adjective ends with に (e.g., 爽やかに "refreshingly").

結果は今ひとつでナンパにも技術が必要だと身にしみた。

This is a rather simple compound sentence made by joining the following two sentences using the te-form of だ:

結果は今一つだった。ナンパにも技術が必要だと身にしみた。
The result was less than satisfactory. I realized even nampa requires some skill.

This 今一つ is a lexicalized no-adjective. If this で were 様態のデ, 今一つで would have to modify the following predicate, which is 必要だ, but "I realized I unsatisfactorily need skill" would make no sense.