I agree, I think the cute concept twice had before allowed nayeon, jihyo(she has a deeper/fuller voice), momo, sana, and mina to shine as they all have bright and airy voices. As a result, members like jeongyeon and tzuyu with deeper tones and even technically better vocals than some of the aforementioned members were stuck with very little lines. They've been able to shine in recent years due to their more mature tracks like 'I can't stop me'/'alcohol free'/'132'and more recently 'moonlight sunrise'. Dahyun and chaeyoung also were also sidelined but the lack of jeongyeon's, tzuyu's, and jihyo's(she's never gotten enough lines for a main vocalist) strong and stable voices really hurt the group overall. The lack of these 3 throughout their entire discography has had a lot of drawbacks and were seeing ripples of it till now. Songs like 'scientist'/talk that talk/ weren't bad they were good but imagine how much better would they would've been had they utilized their more mature sounding members on these tracks. So ultimately Twices' concept can mature and change but the group also has to adapt to the songs and not rely on their high-pitch/bright vocal members as much. As for itzy, they are utilized pretty well overall. Their strength has always been fun/energetic/shouty/chantie dance tracks so the members really excel. Lia always shines in ballads but it is what it is.