I'm just looking back on The Flash, Daley and Goldsmith were hired in January of 2018 with an intial release date of 2020. Had they stuck with the timeline, they probably could have had filming start in March of 2019 and released it in like January or February of 2020, before Covid.
Unfortunately, Ezra's oh-so memorable role of Credence Barebone in the box office juggernaut franchise that is Fantastic Beasts conflicted with the filming. So, rather than recast Ezra in FB or preferably in the Flash, it was imperative to have him in both movies. So they kept Ezra in both of them and moved the movie back to 2021.
Then Ezra decides to go AWOL and starting pitching his own script causing Daley and Goldstein to walk away from the project and delay the project once again./
Had they just recast Ezra in October of 2018 in either Fantastic Beasts or the Flash, they could have had the movie out before Covid, before Superhero fatigue, before the likes of WW84 and Black Adam, soured the market on DC movies in particular, for much much cheaper (Daley and Goldstein's script was much simpler than what the Flash eventually became), and, most importantly, turned a profit.
If the Daley and Goldstein Flash cost 120-150 million, even if it released to the same mixed reception that the 2023 Flash released to, it could have done like 500-600 million worldwide in the 2020 market.