The problem Gunn has is that most stories coming about Legacy are about other characters in Legacy and not so much about Superman. More and more Superman fans are worried about Legacy not focusing on Superman as much as it should. If you look at the rumored projects another Superman film is not on the list. Yes, they're just rumors but Superman fans see that and wonder what is going on with Superman. As this CBR article notes:
It's unclear where the rumor about Superman's reduced presence in the DCU or Supergirl potentially taking over as the universe's top hero came from,
though Gunn has yet to clarify how much Superman will appear in future DCU projects. The speculation also comes amid Supergirl: Woman of Tomorrow cast House of the Dragon star Milly Alcock as the eponymous heroine. Alcock will make her debut as Kara Zor-El in Legacy opposite the Last Son of Krypton.
Until Gunn says something proactive re: Superman and his place in the DCU doubts will remain. Gunn is not known for his honesty and that doesn't help the situation.
https://www.cbr.com/superman-legacy-...-place-in-dcu/