Definitely post-kwangya to me. I liked them from debut, but when My World dropped it felt so refreshing to finally see them shed the concept. Then Armageddon showed what was possible with much darker tones.
Kwangya-era was probably peak “SM” style with the gibberish lyrics and quirky songs. There’s probably an evolutionary line you could track through S.E.S Dreams Come True > BoA > f(x) > early Red Velvet > Kwangya Aespa, as being the distinctive “SM sound”, whereas groups like SNSD and Hearts2Hearts sit outside that and have a more traditional sound.