It's not that they are super impactful it's that wow has always had a ton of relationship stuff and it even takes senator stage from time to time, and no it's not just 4 those are just the most notable ones with big named characters.
off the top of my head there's.
mankrik and his wife
Kalecgos and Anveena
Lor'themar and Liadrin
Kael'thas and Jaina
Draka and Durotan
Ner'zhul and Rulkan
Sylvanas and Nathanos
Vereesa and Rhonin
Alleria and Turalyon
all of theses characters have pretty major story beats based around there relationships and all of them are big players one way or another (other then mankrik) and there are likely tons of other relationships both major and minor through out wow or characters who are defined about losing one half of there relationship.