While I have no intention of applying to Cover, I did take some time to think about how one should approach the situation of being in Holostars (JP or EN).
The primary issue I think for the Holostars is they don't really grasp what Cover is, in totality, and, as a result, don't leverage it all that well. Cover is: a technology company that, to push their tech forward, has a massive Japanese Idol-like branch of streamers using a hybrid of 2D and 3D models to present their entertainment. This means Cover also is a massive Music Publisher by number of releases of original, wholly owned music.
What's the audience for 2D / 3D Vtubers? Heavily male skewed.
How much of a problem can unicorns be? A big one.
So, that ground work lends itself to going in a few directions. You actually need to build a male audience while also dragging in a female one in the process. Most of the HolostarJP are a pretty balanced audience, per a few of their statements. This means leaning into areas with something like 70/30 Male/Female appeal, while still doing activities that lean hard to one side or the other on the regular. (Cover should have some fairly advanced analytics on Who Watches When, which would tell you when its best to do certain activities.)
This is why those WoW streams were doing really well. MMOs have that 70/30 split. But it also means their music direction/approach has normally been very bad. I'm not saying everything should be a dance song, but I am saying a lot more of them need to be. And, with access to that much original music, I'd be releasing Remixes of the tracks I can get access to in the CityPop or Dance Pop styles almost weekly. (I also think very few, if any, Cover vtubers actually leverages their Memberships well. That's where you should be testing out things.)
I actually think Flayon is finding a niche of being the Degen Game player, though the fact he got stuck with the twink model actually makes that work better. Plus he collabed with Rin, which was a solid move. Though I do think most in Cover don't realize that their primary advertising is the YT Algo, which means Network Effects are huge for improving their audience. They don't need to go full Ludwig and show up everywhere, but it matters.
While I'm taking this from a Business Analysis view point, I do also want to note that there is entire areas of YT content that they aren't even attempting to bridge over to. I think that's mostly due to the deeply introverted game players that is both most of the Vtubers and the Management of Cover, but the male Vtubers should really look into branching out quite a bit. There's the occasional break out, like when Azki dove into GeoGuesser, which probably made her 1/4 mil USD. (GeoGuesser is like a 95/5 Male/Female split area of YT, which is why it was perfect for one of the girls to go into. Helps she's really, really good.)
This is a long way of saying I think Ame is the only Cover Vtuber to understand the nature of what the opportunities present for both her own creativity and money making. Suisei has a pretty good read on Cover as a springboard.
I injured my ankle a couple of months ago and had a long time to sit and watch Vtubers (I signed up here not long after). I had time to think about what they could do to improve the situation.
I dunno, right now, I feel Cover has moved on from the technology company model. Right now, and this is reflected in the CEO's own interviews, Cover is a merchandising company using 2D video game streamers as their IP, and providing them with 3D and music production opportunities. Even their future projects like HoloEarth are in service to selling merch or digital goods based on their IP. If you look at the business model, at no point in the future is it likely the tech itself is going to be the product.
In that sense, the unfortunate thing is that everything extra a talent tries to draw from Cover has to be in service to brand development. So sure, Cover is a massive music publisher. But at the same time, even talents quite successful in music don't really make enough from it to be self-perpetuating, and mostly benefit from personal brand development or audience expansion. Kiara for example, every single one of her originals has broken 1 million YT views and most are in the 3-4 mil range, yet she is on the record that her quite successful music about breaks even, and she does it because she wants to and to keep herself in the game.
So sure, someone could publish weekly or biweekly remixes and monthly originals... if they self-funded them, which few talents in the company can afford... or if Cover already saw them as a Suisei/Calli-tier artist and had a larger vested interest in pushing their careers. The only way to make it work would be someone who can self-produce music, which StarsEn doesn't have right now. Or you could also argue that Cover themselves should change the model to fund and push even more music, which I would be in favor.
I generally agree on the audience issue, that's part of why Tempus were initially received so well - the "group of bros" dynamic drew the existing male audience while still able to draw on women. But finding the right programming is the Achilles heel of most creators, and while corporate vtubing tends to dabble too far on the side of shallow content, there's also a risk that when people do branch out they instead niche themselves straight into a black hole. This is how you get people like Baelz spamming out twenty-two streams of Persona 5, or Finana playing nothing but Honkai, FF16, and the Somnium Files for three months straight. And sure, that's horrible for business development, but the creators aren't thinking that way, they're often perfectly happy where they are. Corporate games permissions make this even more difficult. For example, Lando recently jumped on Genshin, which is a great mixed-audience anime game that's currently popular... but not possible at all while under Cover.
That said it's true that there are huge, non-gaming sections of YT where there's no reason a corporate vtuber couldn't succeed. I think the best talent in the company right now in this regard is Shiori, who has done exactly three solo gaming streams total since her debut almost four weeks ago. Of course for StarsEn in particular, Vesper ended up torpedoing the D&D game by getting suspended, and the first form of the Tempus podcast also fell through (possibly for the same reason), so it's not like they weren't trying, it just didn't work out.
You're not wrong about network effects either, but of course those only develop if a group does enough together to be known together. I think the best example of outside-collab network effect in the entire company is Roberu, who is basically known now because of his outside-company collab partners. Is there anyone else in the entire company who does enough outside the company to have benefited from it? Maybe the Trash Taste collab as I still encounter people to this day who were introduced to vtubers through it.
Allllllll that to say, I think there's a lot of competing interests in talent preferences vs audience growth vs overall brand development that get in the way of taking full advantage of Cover's strengths and opportunities.