The Harrier is more than capable of facing 10.7 aircraft, even more so than the Hunter F.6 has past weeks have shown.
It is better positioned at 10.0 for now, but we will continue to monitor how it does.
This already exists in quantitive matchmaking but only works at a full +1.0 BR. Its not possible to make it work specifically at 10.0 for only 0.7 BR.
Something has been done. Harrier GR.1 like all other strongly performing aircraft has had its BR raised. The Harrier was not the first to have this done nor an exception to the rule and we are not going to start revolving the game around the Harriers comfort. It is still more than capable at 10.0 and far better balanced. Other 10.0 aircraft face 10.7s and so must the Harrier as do 9.7s on occasion.