in / at / on holiday [+holidays] | WordReference Forums

I see the reason for your confusion. The sentence that you quoted from my #18 uses the phrase “the holidays” but not in the sense that I had in mind when I was discussing “at the holidays” in #7. In #18 , I was using it to refer to “the holidays that the speaker is referring to” as opposed to “the general time during which these holidays are celebrated”.

The sense of “the holidays” in the phrase “at the holidays” is as follows:

In the U.S., the holidays are those that occur toward the end of December, primarily Christmas and New Year’s Day along with their respective Eves, but also encompassing such holidays as Hanukkah, Kwanzaa and the Winter Solstice. The phrase “the holidays” is used and understood in this way even if the grammatical conditions that usually call for the use of the article the are absent.

Holidays that occur at other times of the year, such as Easter or Independence Day, are holidays but not the holidays.

At holidays can be used to refer to the winter holiday season (particularly, as I’ve discovered from Google, in headlines and titles, which often omit articles for reasons of space and/or style), but may also refer to other holidays. At the holidays refers only to the winter holiday season, particularly if other qualifications are absent.

I really think that this detailed description is more informative than any example sentences I could come up with.