The Second Idea I had to find of make things a bit better is to try tweaking the government forms attached to the religion or culture. Or perhaps the religion it's self.

The simplest way would be to add the ability to raid tribes of the same religion. But maybe restrict raids by culture?

Alternatively more religions could be added to the religion group that are mostly the same. But I think that would be clunky. And it would probably be better to start by fleshing out fewer religions a bit more.

Tweaking the succession laws and government type would be cool but a bit more advanced.
I think having tribal confederations form naturally would be pretty cool.
Which would probably be elective tribes to start. But I could see some hybrid between that and some of the strength focused governments that some tribes in eastern europe have could be interesting.

I would probably peg the new succession laws to culture if I just added that. Like how tanistry is enabled for irish culture characters. Although, that might cause issues for multi-culture tribes. So a new variant of the tribal government could also be cool.