Depends largely on the use case I guess. For us it’s been a critical way of managing permissions and automating notification settings for people. Joined group x? Cool, now you have notification settings adjusted for Categories and Tags related to group x, and are allowed to read and reply in Category x.
If someone doesn’t have the same use case as us, I can see how the existing Group functionality wouldn’t seem so useful.
I can’t speak for Invision, but I wouldn’t underestimate how useful this is in Discourse. Anything you can see or click, you can change. For Themes that sometimes means learning a bit of CSS or HTML, but the internet is full of great resources for this.