Variety reported
It seems typical reshoots add $6-$10 million from what I read, not the $25 million reported for Justice League.
Yes, of course I know that. I haven't been living in the Phantom Zone for the past year. The point is, you can't really call that "waste," because there is no uniform standard for how much editing or reshooting a given movie may have to do in order to arrive at the finished work. There's no definable line of demarcation between "enough" and "too much." If it's what the film needs, if it's required to fix its problems, then it isn't wasted. If anything,
Justice League's problem is that it wasn't given
enough time and money to be properly completed, hence the rushed and widely criticized CGI.
A big reason for the inflated costs were because WB panicked at the last minute about the tone of the movie including the ending from reports. They allowed Whedon to do far more than simply supervise the post production of the film.
I don't believe those "reports," because we've been hearing about WB's efforts to lighten the tone since back when the film was in pre-production, after BvS came out. And you're forgetting the order of events. Whedon was initially brought in to write the reshoot material while Snyder was still onboard. It was only after Snyder stepped down to deal with his family tragedy that Whedon was asked to take over as director as well.
There has been a change in WB mindset apparently as going forward it seems WB will try to factor reshoots into the original budget at the start of production of future movies.
That's not a change!
Every big-budget movie these days budgets in advance for reshoots. I mean, I'm staggered how short a memory the public has, because we've gone through this exact same panic over reshoots with multiple big movies in the past few years, notably
Suicide Squad, Rogue One, and
Solo: A Star Wars Story. Every time it's reported that a film is going back for reshoots -- which are a routine and expected practice that is accounted for in the budget beforehand -- fandom has a panic attack over how doomed the film must be, as if they've never heard of reshoots happening before even though it's been only a few months since their last panic attack over reshoots. Heck, there was a
spate of
articles just last year over how reshoots weren't intrinsically a bad thing. People should've learned by now that this is normal. Creativity is not a one-step process. It involves discarding and replacing things all the time. Rewrites, retakes, reshoots, they're normal and routine and desirable parts of the creative process, because they're how you get rid of the parts that don't work and make them work better.