So is this arc just, like, a really slow retelling of the last movie?
Well, it's a side effect of them not changing voices when the characters get older.
Goku and sons get introduced as kids, when the high pitch voices make sense, but then, inexplicably, when they grow up, they don't bother to change the voices.
He's Mr. Bigglesworth.
I doubt it. This is how every DBZ arc starts. Goofy slice of life shit showing you what everyone's life is like, before the threat shows up and they spend the next 90 episodes fighting it.