各ページにカスタムJSを設定するための「on-discourse」JavaScriptに関するフィードバック?

Not true.

If you are not modifying the API (e.g. using 100% javascript) there is no need to use a Plugin which are more cumbersome to deploy and switch out.

If all you are doing is modifying or adding some JavaScript a Theme Component should suffice.

「いいね!」 2