Personally they're also right.
They've killed off Tony Stark, Cap has returned having lived all those years he spent returning to his past, Thor is out there travelling to recover from the massive losses as seen in Infinity Wars so what does that leave us?
Shang-Chi introduces the Mandarin an Iron Man villain, but he's dead I hear you say well make a movie set between Iron Man 1 and 2 or after 3 and use him in that movie!
Same goes for Black Widow, the character is dead in the present, but not the past!
What's stopping them from making such a movie in the near future but set before her death in Endgame?
There's nothing as far as I can see unless they think building the Thunderbolts the same way they built the Avengers will make them as much money.
Will it?