I'm sure the novel covers it better.
I dont think the manhua shows it very well but she does help when they team up. She deals with a lot of the mobs and weaker enemies so mc can focus on the boss battle. She have also been shown to Kills mobs for him to use with corpse explosion.
Well they did interact a fairly good amout of time... and they show little of what she does to help since as always mc is the focus. For example, there was a dungeon they went with a lot of invisible/wind mob and she was the one to take them out. Also, she was the one with the item that reseted the dungeons cooldown allowing him to leveu up 2x as fast as the others. Remember that her Gramps is the same level as his teacher, so she doesn't fall much behind him.
As I said, the focus too much on mc, so everyone else (besides the teachers) looks useless in comparison. Both Yiyi and other girls (he'll have a couple more, it's harem) are actually pretty capable and usually help him in some way even if it doesn't look like much. Tbh what I like most is that they don't stick to him all the time and have those annoying stereotypical personalities. And his sister is full blooded and not in the harem and honestly this is already enough for me to like it more than most.
Also... maybe is just me but I find the level of bragging in this pretty tame compared to most male mc manhuas. We don't get mob guys picking a fight with him all the time cuz they look down on him or because of women... the allied forces don't doubt his strength all the time, they get surprised but more happy that there's someone strong on their side than jealous and angry about someone lower leveled than them being stronger...
So yeah... I see more reasons to like it than to dislike it... still wish he'd change clothes tho...
I don't get how he likes ning yiyi and since when? I mean all she did was riding on his coattail and being useless every time there was a fight.