>>30838003Hololive is interesting in that it really does mix both of those into a single whole.
Obviously, every single girl has their own fanbase. It's unique, and you only get "tied together fanbases" once in a blue moon, like the early days of KanaCoco.
But at the same time, at least on the EN side, those fanbases easily overlap into each other, not so much as a consequence of collabs, but as a consequence of the whole group being within about the same "tolerance range" of each other, in terms of content. The girls are all different and unique, of course, but it's rare to have such a different style that they aren't appealing to at least a good chunk of the other girl's fans, too.
I like to think in metaphors, so I can do it here, too:
Hololive (at least EN wise, not as cognizant of JP's various inter-gen overlap audiences) is like a salad dressing in terms of numbers. They're all unique girls with unique boxes, like ingredients to a dressing, but when they get shaken up, they mix into a full whole very easily, and then after a bit, cleanly separate back into their constituent parts without much issue.
I don't know if NijiEN is more like that, or more like a full mix, where the different groups eventually just stick together into a "I'm here for the group, not for you" box, but I'd love to know.