The excess of rear grip that manifests itself through the rear end hopping was a characteristic of the older F1 chassis, which was a bit soft for a 250 single. Virtually impossible to cure 100%
As you have found you have to drive round it by just giving enough throttle to smoothly break rear traction, any more than that and you get the grip-release-grip-release situation that manifests itself as hopping. Either way it doesn’t make for good lap times and the hopping is tedious, tiring and destructive!
I’m afraid that I don’t have hands-on experience of the newer chassis that Chris Purdie (CPR) produces, but I know that he has been addressing that issue.