It is illusory to expect a perfect matching between English and French tenses.

If enjoying the meal was a recurring event, the second sentence “nous aimions ce repas” would rather translate to:

We used to like this meal

which seems to match your understanding of its difference. i.e. it is no more the case.

With the passé composé, we know the event happened just once.

Note that in spoken French, you would more likely hear:

On a aimé ce repas (passé composé)

and

On aimait ce repas (imparfait)

“Nous avons aimé ce repas.” (1) and “Nous aimions ce repas.” (2) can’t be really explained in the absence of a context.

A One is talking of a single meal ;

“(1)” corresponds to “We enjoyed that meal.” or “We liked that meal.”. The second form is more a statement about the whole function, not so much the pleasure got out of eating.

“(2)” corresponds to “We were enjoying that meal.”. In this case “We were liking that meal.” is not as likely a possibility (“to like” is not usually found in the progressive tenses) .

B One is talking of a type of meal, either a traditional meal such as a turkey meal for Thanksgiving in the USA or such as any other type of meal repeated on some basis, regularly or not, or such as family Sunday meals and again particular cafeteria meals taken every day, but typical ;

“(1)” corresponds to “We liked that meal.”.
“(2)” corresponds to “We would enjoy that meal.”. “We used to enjoy that meal.” wouldn’t be quite right as in “Nous aimions…” there is no indication that the persons involved do not enjoy that sort of meal any more.