Aliens also didn't thematically fit with the first Alien. As the title indicates, there are many aliens not an alien that was alone. Burke was also a civilian, so Ripley was not the lone civilian. And at the end of the movie she was not alone unlike in the first one. Well I guess Jonesy made it out ok, so she wasn't alone at the end of the first one either.

Aliens was not thematically consistent with the first one and that's what made it great. There really isn't a mystery about the Alien and how dangerous it is after the first one so trying to recreate it wouldn't work. So instead of working class people being forced into a situation they didn't understand and weren't prepared for, we see a group of well armed soldiers going into a situation they were briefed on. This time the humans are going to kick ass! Except no, they get their asses to them. And themes about motherhood can be added (both for Ripley and the Aliens).

Alien 3 wasn't entirely thematically consistent either. I do remember it exploring some themes about religion (it's been a long time since I watched it tho) which is something the previous movies didn't go into. Also Ripley dies at the end which inconsistent with the theme of survival.

To me story is more important than themes anyway. If Ripley has to be alone at the beginning of every movie it makes the story of her character really boring.