Dude, drop the beef. We've been called out on it and I was trying to bring it back to civil discourse and discuss the advantages of adding one or the other. I'm all for both, but I see a lot of redundancy in having both that we don't get to the same degree with other tags.
As you've said, the largest-use tags are litrpg, cultivation/xianxia/wuxia (they are often used together, so no worries about the grouping thing) and smut (again, just grouping because there can be overlap). Here's the problem with polycules and why polyamory works better: A polycule could be heterosexual just as easily as it is homosexual in nature. It's not a Greek or Roman orgy where everyone's doing everyone, it's a "I'm comfortable with this, but you do you and we'll all be together" thing. In a way, it's more like a post-modern take on a harem. With a harem, traditionally, the man takes a wife and is only able to take another wife if the first is agreeable to it. If the first wife does not approve of the other woman, then it doesn't happen (in modern times, ancient times would be "man says so is"). It's more of a business transaction than it is romance. Mormonism is similar in that there isn't necessarily any love between the wives other than for the husband.
Polyandry and polygamy are both flavors of polyamory, but are also exclusive of romance between the primary person and each individual. Polycules are primarily used in LGBT+ novels and typically don't contain hetero matches, but are open to the possibility in the form of bi-amorous members of the polycule and that's something that isn't accounted for in the tags currently or with a polycule tag. Polyamory would include that dynamic naturally as all members are romantically involved with each other, but still leave the option for bi-amorous members to explore in an open relationship without the fear of losing everything (leave your husband as a mormon, you're out of the church if my understanding and recollection aren't wrong...I'm not mormon and have no idea what the actual rules are beyond the absolute basics).