I agree with this.
Superman is still too big an unknown factor for the Legion to be brought in right now. Is Superdad really from an alternate reality or a changed timeline? What were Nuperman and NuLois? Were they real? Versions taken from another world to fill in while Superdad was stuck on Telos? Temporal echoes? Clones made from sand? What's the deal with the powerless Clark Kent? Why are villains like Doomsday showing up from a reality that has either been changed, or no longer exists?
There's no way you can do the Legion until you answer those questions.