It seems they started their career with an edgy, hardcore rap concept. They had a “fuck the mainstream” message.
Then they shifted to self-introspection (personal life struggle rather than social struggle) and because that made them popular they stuck with it until they became really big worldwide.
Post-Billboard era they tried doing that artistic shit, ie. thing they did with the ballerinas. But obviously they learned from Western music producers they have to change their style to fit American music tastes, in their capacity to do them. They wouldn’t be able to compete with a rap heavy crowd so they did the sappy, high pitch “my life is rainbows” > IDOL > Dynamite > Butter > Permission to Dance. With their B sides as a recapping of their previous song styles.
Whoever the “real” BTS were they are most likely found somewhere in the early years.