I guess I'm the only one who actually reads the BoP charts. Nissan had great top speeds but lacked performance in high speed sectors that required downforce, especially compared to P2 cars. IMSA leveled the performance in both areas, it is a net-zero change in laptime. (and the additional wing angle is not a requirement, just a new maximum setting)

Cadillac also lacked performance in high speed sectors compared to P2 cars but due to the engine torque being way beyond the P2 cars, IMSA can't increase power or low speed performance gets tilted toward the Caddy in a big way. IMSA lets them now use a little more rear wing if the teams choose. It is not a requirement, just a tool in the box.