There’s definitely merit to “it’s their first time being parents” parenting is really hard and just because you were a child to parents before doesn’t give you experience parenting. Same as being a student in school doesn’t give you explicit knowledge on how to teach a classroom, you have to learn by doing and that takes time.
That’s when people use that phrasing. When they do something harmful. Or when the kids go no contact. It’s always “well they’re your parent!” “Well they’ve never been a parent before!” “Well they learn from their mistakes!” No. If you don’t have patience, if you have a bad temper, etc, if you can’t be a good parent, don’t fucking have kids. It’s a choice.