I see it as having three main threads going on, each of which could've been their own manga:
A) dude seeks revenge for his mother's death
B) teens finding their way through the entertainment industry
C) expo about said industry
Apparently it's got romcom stuff as well, iunno.
Anyways, the issue is that the main hook is A, it's the climax of episode 1, but the story is actually centered on B and C and that's why I think its advertising was disingenuous. You always have to go into a work knowing what it's about, because if you have the wrong expectations you'll come out upset that it wasn't what you were looking for, but this time the show itself
and everything surrounding it plastered Ai's face everywhere it could and is now failing to deliver on it. I assume that's why >>108520
called it filler, even though... it's not, not at all.
For example, for comparison, Perfect Blue doesn't stop every ten minutes to dump some exposition on you, themed kirara doesn't have super srs dramatic character arcs, and something like Pompo had its protagonist's goals and his learning about the industry perfectly aligned, as well as being more of a pure celebration. OnK indeed tries to do everything at once, which is why negative reviews keep saying something along the lines of it being unfocused.
Also, I don't think any of the characters so far are as interesting as Ai was, and that's a shame.