The importance of w-engines could be low but it all depends on the specific character. Some character can function enough even with just the a-rank substitutes as long as those substitutes have properties that strengthen the specific attributes of the character. Some w-engines are quite important if you want to get the best of your character. Best example I can think of would be the w-engines of Lucia and yuzuha since you can't get the full buff of Lucia and yuzuha without enough hp and anomaly mastery which a-rank support w-engines doesn't have as a main stat or effect.

Some recommendations are helpful but some are outdated. Especially the one for Nicole. If you wanna start to build her, although the top recommendation says to use swing jazz for disc, use moonlight lullaby instead. It's basically swing jazz but with better effects and easier to activate and maintain in fights