There are lots of options, which is what makes it confusing, none are right or wrong, as long as you get the balance you like and lap times are on pace.
However...If the rear tire is lifting and your running low rear roll center already, then it has to be springs. Since low RC is the most chassis roll (least wheel lift potential)
Keep in mind all the roll center changes in the world won't help overcome the incorrect springs, since roll center changes effect the leverage the chassis has on the shocks.
Ie; remove your shocks and roll the chassis by hand, change roll center and repeat. You'll feel no "stiffness" change, but you'll get to see how camber curve and roll center go hand in hand.
The more the camber changes, the less leverage the chassis has on the shocks to compress them under load. High RC. Ideal with lighter springs in bumpy conditions. And vice versa.

What I would do is consider the feel I like, where it happens on the track and the available traction. Also, the springs I'm running at the time.
If I like the feel or balance of the car I would try one spring up on the opposite end first, since it's an easy change.

I've had great luck using roll centers and camber link & shock locations similar to what the factory guys are running in similar conditions and tuning springs and oil for the feel and weight transfer speed I want, as well as static camber and ride height.

.....
I remember seeing Matt Francis at the nats in Dalton on two wheels in the sweeper at speed. BOTH inside tires off the track, lap after lap! That's good balance! lol