TBH I have no idea what the status of the Legion is at this moment. I'm not entirely sure that even the writers know what the status of the Legion is at this moment, but I haven't read Legion of Three Worlds, which may have resolved it all, so don't take my word on that.
The Zero Hour reboot was meant to reconcile the Legion continuity (still lagging in pre-Crisis) with the new post-CoIE main continuity - Superboy no longer existed, which meant he could no longer be the inspiration for or a member of the Legion, who therefore became modeled after Mon-El. AFAIK that was still the status quo when this story was written. Geoff Johns has, very, very recently - like in the last year or so - brought Clark-as-Superboy back into continuity, and it looks like we're moving back to the "Clark is the Alpha, the Omega, and several universes cooler than anyone else in the history of anything ever" of pre-Crisis, but I plan to ignore that as long as humanly possible in the hope that someone will realize what a bad idea it is and make it go away before it can take. Either way, the point stands that up until ICk, "Clark as ultimate symbol of hope and therefore more important to the fabric of the DCU than anyone" was in Diana's head more than any kind of objective truth.