According to the screenwriter for the movies, Chris Morgan, they expected this "face turn" for Shaw to generate a little controversy.
Link to article but relevant parts copied below:
ENTERTAINMENT WEEKLY: You joined the franchise writing the screenplay
for Tokyo Drift, the movie that introduced Han. When we first met
Deckard, he was killing Han. How did you guys decide to turn his
character in this film?
CHRIS MORGAN: There are a couple of things I would say. We don’t know
his full story yet, so there are things we’re going to learn that I
think will be cool when it comes to light.
Beyond that, I would say, Deckard’s character is not that dissimilar
from Dom, in certain ways. The reason Dom went to jail in the original
film is he did some violence against someone who hurt his family.
Deckard’s story is not too far away from that. The reason he comes
after our guys in the last film is because he has a similar code, and
he looks after family. So at least there are some markers in there for
these two guys. That felt like you might be able to turn him, in a way
that you could start understanding what his motivations were.
I’ve got to tell you, I love him in this movie. I love him and Dwayne.
I love the way he relates to the team.
EW: When you guys initially brought him on in the last couple of
movies, was there always some notion of flipping him from an
antagonist to joining up with the team?
CM: Bringing Jason into the franchise, we always had an understanding.
His character is a man with a code, and he believes in it, and he has
a lot of similarities to Dom.
There are things, as developers, that we know about the character that
you guys, the audience, do not know. We have the luxury of getting to
that. I think people will be surprised and interested in it. This
movie gets to a little bit more about who he is, and we learn a lot of
new things about him.
I think the response will be that, because of what happened to Han,
there is going to be a residual drama and tension. We’re going to lean
into that. We haven’t forgotten about it. We’re going to investigate
all of that. But also, you can see, in this film, a little more in
[Deckard’s] core, as well. I know it’s a little unsettling, I know
it’s a little different. Maybe the audience isn’t expecting it. I
think it’s all, in the end, going to be a really exciting, fun,
valuable experience. They’ll come to understand.
It sounds like the upcoming movie(s), presumably including the Hobbs and Shaw spinoff will go into more details around the character and provide more insight into the new "team" dynamic. Plus, saving Toretto's son definitely earned him a whole load of brownie points.