All vehicles introduced to War Thunder have a dynamic Battle Rating, meaning they are never fixed in one position and it has been this way since Update 1.37 in 2014. If a vehicle goes down in BR, it means its statistically not performing well and if it goes up in BR, it means its performing above the average for its BR. The Harrier GR.1 is able to perform exceptionally well at 9.7 and thus, its BR was raised to 10.0 where it is still able to very well, but is more balanced here and is still very much able to do all the things it did before.
Regarding repair costs, they are calculated based on the earnings people make with a vehicle. For it to have the repair cost it has, it means people are typically earning far more than that with it in battle on average. Should that income level change, then the repair cost will be adjusted in the next economy patch.