What mistake did they make?

They said Several Months Later when I remember when they said 6 months after Buu they used the Dragon Balls to make everyone forget about Majin Buu and then some time passed. Super is likely to start at Age 778 and the Future Trunks saga is at 780 (Seeing that Trunks went 17 years back into the Past).

Super starts 6 months after Boo and the Black Goku arc is like a year and a half later. It's kind of annoying as Pan was born 5 years too soon.

Did they change Goten's voice? It sounds kind of different.

No, Kara Edwards is still Goten and Videl. I believe Trunks has a new voice though.

Buu saga Kai's dub is pretty great too. The Green Tint is still there, but it does not bother me that much. I don't know why Toei added in it in the first place, but it could be that Buu saga Kai was a cheap project and was meant to be direct to video (It air on TV due to Toriko doing poorly on the last minute).

Didn't the Japanese version of Boo also cut out like 10 more episodes worth of filler compared to some Chinese cut?

The US is getting more episodes of Buu saga Kai compare to Japan. So Buu Saga Kai won't end on Toonami until July 2018 since we're getting the International cut.

The Future Trunks saga in Super probably get dub until early next year. The American fans will have to wait for the Universe 6 Tournament to be dubbed until August 2017.

Ewwwwwwwwwwwwwww. We don't need to the longer version of Boo because the shorter version was still already too long. I mean, they were doing half a manga chapter per episode in that arc. There's no reason why it shouldn't be 40 episodes at most.

Unrelated to everything, but how did the Ginyu Force end up on King Kai's planet?