I guess understand this a bit. As a man I tend to use a deeper tone when I’m being more serious and I use a higher register when I’m being more casual. So it makes sense that women would be advised to do the same even more so if they’re trying to be taken seriously.
Still I’m not sure it’s actually effective. For myself, I feel like I only use tone as an indication of seriousness relative to the speaker’s regular tone. If a female co-worker consciously switched to a lower register all the time I feel it might backfire as it would be harder to tell when she was extra-serious. Though you have a much better perspective than I, I didn’t even realize that was a thing women did.
As for Holmes, she’s actually taken it to uncanny valley territory. If I was talking to her I think I’d actually be distracted by “WTF is going on with her voice”.
