Is the poor handling of the Vanguard series at the moment intentional?

It was intentionally reduced from its 3.9 levels, and again, it's had another pass this week. It was a little too harshly tuned down compared to 3.9, so it's had a little bump back up again. It's still a very effective fighter if you look at all the metrics for it. The Vanguard owners are caught in this weird cycle of they hate their ship, but it's an amazing ship to use and fight with, but they hate it.

They didn't specify here, but the handling, are they talking about atmospheric stuff or are they talking about space as well?

Probably space. It was slightly a bit too sloppy in its rotations. It's the technical term.