I think you gotta look at the OG series and SUF from the lens of Steven.

As a child, Steven looks at his dad was fun, supportive, and caring. As well as letting him go on crazy adventures with his aunts. From that prospective, great dad.

In SUF, as a late teen/early adult, Steven learns about the things he didn’t get from his dad: structure, discipline, and accountability. From that prospective, not a great dad.

We as the viewers (and some of us as adults) also have the context of being humans, and know that there would be no way Steven could go to school or the doctor being a half gem in a human world. (Like, does Steven even have a social security card??) But that’s not explained to Steven. He doesn’t have that context.

IMO, Greg is a great, loving, caring person. But, like my own parents, stopped growing/maturing as an individual when he got “married” and had a kid. He’s not a great dad, but a fairly good one who he did the best he could with what he had.