方便: a "skillful means" of translating upāya or not?
The meaning of 方便 (In the viewpoint of Buddhism)

明代《三藏法數》
方便
方即方法，便即便宜，猶善巧也。

or

清末民初《丁福保 佛學大辭典》
方便
方者方法，便者便用，便用契於一切眾生之機之方法也。又方為方正之理，便為巧妙之言辭。對種種之機，用方正之理與巧妙之言也，又方者眾生之方域，便者教化之便法，應諸機之方域，而用適化之便法，謂之方便。

The above content is translated in 《Soothill-Hodous Dictionary of Chinese Buddhist Terms》 as follows.

方便 upāya
Convenient to the place, or situation, suited to the condition, opportune, appropriate; but 方 is interpreted as 方法 method, mode, plan, and 便 as 便用 convenient for use, i. e. a convenient or expedient method; also 方 as 方正 and 便 as 巧妙, which implies strategically correct.
……
The meaning is-- teaching according to the capacity of the hearer, by any suitable method, including that of device or stratagem, but expedience beneficial to the recipient is understood.

Who came first?
One argument is shown below.
“方便”一詞的來源，你知道嗎？
第二段第一行 The first line of the second paragraph:

“方便”源於佛經。它的本義指佛普渡眾生時所採用的各種方法、手段。

&quot;方便&quot; is derived from Buddhist sutras. Its original meaning refers to the various methods and means used during the Buddha's salvation.
最後一段第一行 The first line of the last paragraph:

施行方法、手段、見機行事，其目的、結果就是與人便利，使人舒適。所以“方便”又引伸有便利、舒適、適宜之義。

The purpose and the result of the method, the means and the action are to give convenience to people or to make people comfortable. Therefore, 方便 is extended to convenient, comfortable or appropriate.