First of all it's an anime, an old comedy-leaning anime at that if we talk about Kanto, so the same rules for the protection of real people do not apply for its characters (Ash could be burned to a crisp by his Charizard, thrown through the air by Misty and all sorts of other things and in the next second he's alright)
Ash is the classical idiot hero of older animes like that, and most of the trouble he gets in is caused by himself because he's either too stupid to live or he keeps insulting people (like Erica). And thise kind of characters get pain inflicted upon themselves in shows like that.
Both Ash cluelessness and Misty's "abuse" (honestly it's really cheapening the word and the real world problem to apply it to a comedy anime like the Kanto Saga. Might as well call out Jerry for "abusing" Tom. ) are over-the-top in such a way that it bears little resemblance to real life situation. And Misty was often enough shown to be a friend to Ash when he wasn't acting too stupid to live.
And since I found Ash a rather grating character I enjoyed him getting his comeuppance from Misty.
Its not considered abuse because Ash isn't affected by the slapstick he receives. (By this I mean he doesn't take her insults or physical brand of slapstick to heart, he's not upset or feels abuse) In actual abuse scenarios the receiver is clearly affected/hurt by the actions of their abuser, Ash doesn't take offense to anything Misty said/did nor was he ever not in an unfair power dynamic. (Ash would have to fear Misty or take her insults/slapstick as a means of direct issue) In fact Ash himself would even have moments where he would throw insults or argue back at Misty, thus giving them an even playing field. Its also not like Ash didn't deserve a lot of the slapstick either, as he would often say insensitive, stupid or insult Misty, which would prompt her temper against him. Compare Misty's insults to Ash and her insults toward Psyduck Pre Hoenn and you'll see the difference.
Idk why people get this idea or have to be SJW on something like slapstick, because they like to insert "gender equations" into the argument. Its not like they are portraying an abuse scenario, its literal slapstick. Characters in anime/shows get comedically hurt all the time. So by this logic would Tom and Jerry be considered a show about "animal abuse" because it features an animal duo who's purpose is to literally slapstick each other?
If people want to go farther, anytime they've used Pokemon to assault or attack Team Rocket could be considered "abuse" considering it often involves Electrocuting or physically hurting TR to the point where it does affect them, at least depending on the writer. And being bad guys doesn't excuse it, because that's like if police officer physically assaulted a man by beating him for stealing. I don't take this personally btw, I'm just using it as an example.