As a gidle fan, tomboy is really among their weakest title track. The top tiers are Hwaa, Hann Latata and Lion.
I Burn remains their best release to date.
Soojin's voice does make a difference in my opinion. Like OP pointed out, the group now lacks someone who bridge between the girl crush members Yuqi, Soyeon and Minnie and the softer girl Miyeon and Shuhua. Soojin is very versatile. She is feminine but she can be badass too