According to Nvidia [0], DLSS4 with Multi Frame Generation means "15 out of 16 pixels are generated by AI". Even that "original" first out of four frames is rendered in 1080p and AI upscaled. So it's not just 3 extra frames, it's also 75% of the original one.

[0] https://www.nvidia.com/en-us/geforce/news/dlss4-multi-frame-...