I like this controversial change from the books
This is controversial, but I actually really like how they made Garrett's dad a real person rather a one dimensional trope of an abuser. Because in reality, most abusers aren't one dimensional- they are generally normal people you would not think twice about from the outside, who are also an abuser. They have many similar layers as the rest of us. And I am not saying that in order to soften the weight of abuse or make him out to be redeemable. Its because when books or any sort of media really makes someone out so that their abusive demeanor is the only character trait they have, it honestly undermines the stories of real victims and makes it easier for people to stay for longer than they should or make excuses, because they struggle to hold the multiple realities of their abuser (or other people's abusers) at once. Garrett's dad is a one dimensional trope in the book- not a real person. This is largely not reflective of people in real life. Garrett's dad in the show is a real layered person, who is ultimately an abusive POS too. And while that is the most important thing about him, it's not the only trait about him, which helps to ground us in the reality of abuse. Which helps us give empathy for why his girlfriend won't leave and for why Garrett's friends don't clock it. And this REFLECTS REAL LIFE. So I actually think it was an important change- the changes don't mean they are trying to give his dad a redemption arc. They are reflective of clearly trying to honor the real experiences of victims and the painful reality of abuse.
That being said, I do wish we got "the first time my dad hit me was on halloween" scene. I think they could have done that and still done all the above, easily.