When did gift bags at parties become a thing? When I was a kid the social contract was "I host the party you give me a present, and next time you get one".
When my kids come home with gift bags I feel like screaming.
I think the trend of gift bags comes from a good place. Parents saw that when the birthday kid gets everything, it's easy for that to become a lesson in selfishness and Main Character Syndrome. Having the birthday kid also give gifts to the guests helps make it feel like a shared experience where everyone is important.
i have the impression that in china gift giving for birthdays is less common (in general most gifts are red envelopes with money anyways). as a consequence there is no expectation for kids to bring a gift when they attend a party.
as a parent i would make that explicit, in order to be inclusive, i would ask/demand that no presents be brought to the party. any friends or family who do want to give a present should do that in private before or after the party, and all present are also to be opened after the party when the guests are gone.
that avoids a number of problems. the birthday kid can focus on the party and the guests instead of being focused on the presents. any disappointment about the "wrong" presents is hidden from the giver. givers won't be embarrassed or judged in front of the party if their present is somehow inferior to others. or givers can't brag about their cool present, and also the kids can't show off what cool stuff they got. really wrong presents can be ignored, returned, passed on without any fuss....
The plastic junk is just collateral damage.