Responses
One: Jian Yi and XiXi aren't the Og couple or the main couple. This story has 2 main couples making up the one day band. 2: their story could have progressed earlier when Jian Yi confessed to XiXi but it felt like nothing really changed even though Zheng Xi came to know everything. On the other hand, Tianshan are the more favoured couple cuz their story is more intriguing to the audience.
I've seen some people complain about the frequent appearance of Mo and He Tian. It's true that they're being covered a lot more these days than the original couple, but personally I'm quite pleased with that. I find them far more interesting and refreshing. I love their chemistry and constant banter. The two are also a lot more intimate than the other couple, who still mostly act like friends. That's not to say that I dislike Jian Yi and Zhan Zheng Xi by any means - I don't - it's just that their relationship is not really progressing and so I find their scenes boring at times.