Thanks for asking! Getting misgendered is different for everyone and heavily influenced by factors like age, weight, how far into transition someone is, how much they pass, etc. I've been trans for a long time I'm in a pretty comfortable place, but I still get misgendered on occasion.
How "bad" it is mainly depends on whether there is malice behind the misgendering. An honest mistake is excusable (until it becomes a pattern), an asshole is not. In fact, I unintentionally get misgendered the most by allies (ironically) but it's never out of malice. I'd say overall it's similar to your example of misnaming someone, especially since the two often go hand in hand. If it happens once or twice it's not an issue, but if someone purposefully calls you by a different name (presumably one of the opposite gender) then there's a problem. In some states your name and gender are protected, in other states it's legally mandated to be a complete and utter asshole.
Regarding my original comment, it's mainly frustration at the hypocrisy some people have who make every excuse to avoid using someone's preferred name or pronouns, but then have no problem switching when it's someone else's pet.
There's also this meme:
While I have you here: this is tough to hear but please believe us when we say the US is trying to genocide us. The Lemkin Institute for Genocide Prevention has already issued its third warning , but getting people to pay attention has been a huge struggle for us. We're literally just regular people trying to live regular lives.