I'm not saying that i don't want this harem to fall apart, but... We're going way too fast. Raku has just rejected Marika and Haru (kind of) just a few chapters ago. But meh, i don't really care
I mean, if they wanted to maintain the status quo until the very end, this is just how it had to be. And a lot of the side-character crushes relied heavily on one of the main two choices developing far enough that they were in the end-game, as well, anyway.
Tsugumi couldn't have been clued in, I feel, until Raku had already realized he loved Chitoge, in my opinion. Otherwise, he wouldn't potentially have the option of using his actual, real feelings for Chitoge he has developed while in the fake relationship as part of his reason to reject her, because I totally feel like that's a valuable thing for him to admit to her, of all people, before he admits it to Chitoge herself.
Same for Haru- she couldn't have properly confronted her feelings if Raku wasn't already getting more comfortable with Kosaki and talking more normally with her.
It's just an unfortunate fact that these two characters needed the two priority relationships to be virtually at the point of establishment.
And once Marika's arc wrapped up, there was no way to maintain the status quo anymore without her, anyway, so everything was just going to be one arc after the other, focusing on wrapping everything up.
Well, that's just how I'm seeing it, anyway.
Edit:
Oh, nevermind. I guess it was more for Chitoge to be more comfortable in her feelings to the point she could earnestly admit to Tsugumi that she really was in love with Raku, so she could just give up on her own without a rejection.