>>47328761It's a completely different build. Eternatus is built for stalling, with recovery, a toxic immunity, no x4 weakness and Pressure.
Its only good boosting moves, Cosmic Power and Dragon Dance, don't do anything for it offensively.
Naganadel is a sweeper and its ability can be customized to either make it harder to revenge kill, or harder to handle defensively.
Eternatus can't dynamax, while Naganadel is more powerful and dangerous than it under dynamax.