I'm replying to this instead of editing it only because it's an update, and people who have already reacted to the information won't look back on the addendum:
It seems that Rion's ire might actually be directed at NBC Universal and not Nijisanji. A friend of mine who is a Hakache fan told me that it's actually TRiNITY that is being treated comparatively poorly relative to the other Niji members under NBC despite performing better than all of them, and are not getting the same opportunities with concerts/models etc despite fan outcry.
You may think that the timing of the tweet is poor given that it overlapped with NJU Day 2, but TRiNITY's performance yesterday was one of the highlights, so her comments may be reflective of 'appreciating the support of fans' and giving them a taste of what a TRiNITY concert might look like despite NBC seemingly being unwilling to give them one.