While I am sure there is misogyny in play - there always will be in any DV case that involves a woman - I think it's important to consider that:
1) Amber Heard misled people into trusting her, largely based on her being female (just going off her own recording that she said to Johnny). People get more upset when they trust someone and find out they lied to them.
2) The social bias that domestic abuse/violence is primarily, if not unequivocally, caused by men (because said society refuses to take male victims seriously, another downside to the patriarchy/toxic masculinity that permeates our society), kind of broke down here. The people who actually paid attention got to see some of those biases blown apart right before their very eyes. There are some (even on this forum) who had their world view shaken. This is a big deal to people. It causes a lot of emotions. Not that the two are equivocal in any way, but it'd be similar to someone who suffers from systematic racism realizing they're being systemically racist and not realizing it until just now. It shakes up everything you thought and said before.
It's also this bias that tends to make people not as toxic towards male abusers, because they just kind of expect it. Very few people are surprised about a male abuser, that's an every day thing. A female abuser (even though, in actuality, it is also an every day thing, just underreported to the police/news because of how society treats men) is rare, so it catches people off guard.
So, sure, I agree some people are being misogynystic about it. Especially people more in the central/right leaning political sphere, who largely were only rooting for Depp because he's a man and not for any facts about the case.
But I also think a lot of people are just upset about being lied to or upset that their world view has been challenged.