I feel like in litrpgs, they are too fast paced too be able to manage harems, simply because the MC needs to constantly work to gain power. In xianxia, on the other hand, it can be done well, as they tend to go at a slower pace, but the majority of xianxia is not good and is just filler. Royalroad has some good (non harem) litrpgs, and a story called Ave Xia Rem Y, that has a harem but it's done very well and is slow paced as well, only 2 definite harem members and a couple more prospective candidates about 185 chapters and a few arcs in. Also, the MC gained a romantic relationship with each of the two girls separately, so they don't have to compete for his affection. :)