So to put up some context, Billlie debuted last november with a mini album, made their first comeback this february with another mini album, released a special "project album" for a remade song from their CEO one month ago, and it's about to make a comeback at the end of this month with another mini album.
Basically, this mean they about to release 3 mini albums and 1 single album in the span of 10 months, which I think it's pretty insane. Sure, they just debuted and are rookies, groups need to be pretty active the first years so they can make a name for themselves on the industry and build a fandom (specially if they are not from a big company), but I still don't think it's the right decision.
Billlie seems to have built a decent fandom already, specially after the viral factor of GingaMingaYo and Tsuki's whole existence. However, I feel like this virality along the amount of big girlgroups debuting lately is making Mystic Story overwork the girls a little too much for fear of the group falling into oblivion. Billlie has these projects they do every 11th of a month where they often release dance covers which is cool but it also implies a big amount of work. Add this to the fact their own choreographies aren't exactly easy to do and learn and you can understand why I think all of this in 10 months is too much.
There's also another thing: sure, Billlie has a decent fandom, but it's not that big either yet, the project they did last month with Pitbangsu was cool and all, it barely received hype yet they sold +50k albums which is pretty good for what the project was, but when your fandom is this size, and you are in between of getting into a solid +100k zone and groups who are borderline nugu, you do not want to oversaturate your audience, you have to make a situation where the own fandom is the one asking for a comeback and is genuinely excited once it's announced. For the comeback this month, I've not seen the hype I saw when their last mini was announced and I think it has to do with the project of last month being a physical release as well, you do not want to milk your decent sized fandom until exhaustion because once they don't care about a comeback they may not care about future comebacks.
Said all that, I still think Billlie will do well, but imo a comeback at the end of the year (November/December) would have been more healthy and smart for the growth of the group.