With open differentials, keeping both the left and right tires on the ground makes an enormous difference to how far you can make it offroad. Open differentails provide power to the tire with the LEAST amount of traction (e.g., the one in the air spins, the one on the ground does nothing)
Left to right flex in the front was definitely nothing to write home about either. It's a few inchest at most.
The rear did a lot better.
Compare the pictures above to my Blazer at its pinnacle, from a suspension perspective, with 32" tires. Huge flex. It's not even fully stretched out yet and can do better. The top of the rear tire would be almost even with the bottom of the front tire at full flex. That's around a 32" differential. Much better than what the 4runner is seeing now. This is one reason solid axles are a frequent conversion option for IFS trucks.
Here's my Blazer on 36s in a similar situation to the one the 4Runner is pictured in at the begining of this post. Same suspension setup as the Blazer pic above, just bigger tires. The sway bar is connected. Any further up the rock and the right front tire started to come off the ground. This is how good it was in street trim. :-D