Elizabeth Wagmeister and Adam B. Vary, of Variety interviewed 11 people who worked on Buffy the Vampire Slayer and/or Angel, or had inside knowledge of the productions. [link] [Wayback Machine archive, for posterity [link] ]
Interviews that Variety conducted with 11 individuals who worked directly on “Buffy” or “Angel,” or were closely familiar with the productions during their runs on The WB and UPN, painted a portrait of Whedon as a talented, collaborative writer-producer with a pattern of inappropriate, imperious and disparaging behavior toward those who worked for him. Whedon created a “cult of personality” around himself, according to these sources. Those on the inside of Whedon’s circle basked in his attention, praise and friendship; those on the outside got the opposite: scorn, derision and callousness. (Everyone Variety spoke with did so on condition of anonymity, either so they could speak freely or out of concern for their careers.)
Here's who didn't talk to them:
Variety also reached out to 40 other actors, writers, producers and directors from “Buffy” and “Angel” — including Sarah Michelle Gellar, Michelle Trachtenberg, Amber Benson, Eliza Dushku, David Boreanaz and Alyson Hannigan — all of whom declined to participate in this story.
A relatively long piece, it's undated (unless I'm completely missing it), which gets on my last nerve, but Wagmeister [link] [archive; [link] ] and Vary [link] [archive: [link] ] promoted it in (currently pinned) tweets dated February 26, 2021, so I think it must have been published on or right before that date.
The first allegation addressed in Variety is the one Charisma Carpenter put out on February 10, 2021:
A source who worked with Carpenter when she was on “Buffy” and “Angel” corroborated her story with Variety, saying that Carpenter would often discuss the mistreatment at the time, characterizing it as “very, very bad,” “mean-spirited” and “verbal abuse.”
Next up is Michelle Trachtenberg's:
The most troubling statement came from Trachtenberg, who played Buffy’s younger sister, Dawn, on three seasons of the show, starting when she was 15*. In an Instagram post, Trachtenberg characterized Whedon’s behavior as “not appropriate.” In a later update to the caption, she alleged there was a “rule” on the set that Whedon was forbidden to be alone in a room with her.
While several high-placed sources who worked on “Buffy” say they were not aware of this rule, a person with direct knowledge of the production at the time confirms to Variety that an effort was made by those around Trachtenberg to ensure the young actor was never alone with Whedon. According to this person, it was due to an improper verbal exchange between Whedon and Trachtenberg+.
A representative for Trachtenberg declined to comment.
+ Emphasis mine
* Tratchenberg would have been still 14 when she began work on BtVS. I don't know how many weeks ahead of airdate the show shot, but the season 5 premiere first aired on September 26, 2000. Trachtenberg's birthday is reported [link] as October 11, 1985. I'm nitpicking, but months are a bigger chunk of your life at that age.
Relatedly, later in the piece, there's this:
In that high-pressure production environment, the “Buffy” set was often aggressively adult, with inappropriate and cutting jokes flying behind the scenes. One source with detailed knowledge of the production recalls Trachtenberg’s mother expressing frustration because the set atmosphere was inappropriate for a young teenager.
Variety also summarized Ray Fisher's allegations from Justice League and noted that Gal Godot and Jason Momoa publicly supported him. There's also brief mention of Joss Whedon's "abrupt" departure from (WarnerMedia owned) HBO's upcoming series, The Nevers.
Variety adds 20th's butt covering:
Multiple high-placed sources say if there were any complaints about Whedon on the sets of “Buffy” or “Angel,” they never rose to the studio level or became an official matter with human resources. Nor did those who spoke with Variety have knowledge of any payouts or settlements regarding Whedon’s alleged behavior while “Buffy” was in production.
20th Television, the studio behind “Buffy” and “Angel,” declined to comment.
After delving into some of the conditions that might have contributed to/allowed Whedon to play the jackhole (tiny budget with little oversight, relatively remote soundstage, Whedon's lack of experience as a showrunner, largely young cast, yada yada), the piece references ex-wife Kai Cole's 2017 guest blog piece for The Wrap and her allegations about their marriage. [link] [archive: [link] ]
About 1/2 to 2/3rds of the way through, the report cites sources who allege Whedon didn't want to cast CC, resented that he was made to, made it clear he had favorites, and that she wasn't one.
Next, it gets to Sarah Michelle Gellar:
Even Whedon’s top star apparently had difficulty with him. Two sources familiar with the production say that fairly early into the show’s run, Gellar had a severed relationship with Whedon, to the extent that she did not want his name spoken around her. That made for awkwardness on set. Although Whedon moved on from being the day-to-day showrunner on “Buffy” in 2001, he was still the overall executive producer, and was writing and directing episodes until the series ended in 2003.
The SMG-part I've bolded seems like new information to me, but it does not surprise me at all (and might not have, even back in the day). The previous bit about CC's and Whedon playing favorites, and making no secret of who was in and who was out, is how I assumed the set worked, once we learned about their Shakespeare gatherings.
There's a bit more information (Nell Scovell, Jose Molina) that you may or may not have seen as the story unfolded. Overall, I found it well worth the read. I expect it's a decent representation of what it was like to work for Joss Whedon. Ptui.