Yeah I think the author misstepped in making the two already so fallen for each other to the point that they basically have no excuse not to be dating, that they have to constantly reach for excuses to interrupt their relationship progress otherwise the manga's gonna be over in a volume. It would've been easier for the author if the two were further apart and they could spend time depicting how they grow close (e.g. like in the fucking GOAT SoL romcom atm
Ogami Tsumiki)
On top of that, they haven't yet come up with any other real inner pathos or character development that the characters have to work on first which leaves
"oops, sister" as the only tool in their repertoire at the moment, but it starts to stain the sister's character in a way since she keeps being used to hamper the MC.
(Slight tangent, but you see a similar issue with the "wife" character in live action TV shows -- like in Breaking Bad or Walking Dead, the writers end up accidentally using one character as a foil for elements of the main character too much and suddenly fans go "god I fucking hate Skyler" and the writers are like "??? Skyler did nothing wrong! Walt is a bad person and has murdered people!! Why don't you like her???" and well, it's because the protagonist is our POV and Skyler is constantly used to block or irritate him so obviously that gets projected onto the audience, regardless of morality. If she were the protagonist this issue wouldn't exist, but she isn't and storytelling structure and pace matters, so here we are.)