Those vertical end links on the rear sway let it wiggle sideways, forward, and backward. The only firm connection they make between the swaybar and the body is in the up and down vertical plane.

The length of the panhard rod (several feet) and the range of the suspension movement (6 inches at most) means that the side-to-side positioning of the axle doesn't really change much at all even between fully extended and fully compressed. And even then the most movement is only when both sides of the axle are compressed, otherwise when only one side is compressed it hardly moves at all.

If you take off the panhard rod the rear axle will be able to flop to the side until the wheels hit the inner fenders and stop it from flopping further.

Now, if you diudn't have the endlinks and bolted the swaybar ends right to the car, you might have a slight point. But the swaybar isn't firmly positioned side to side by the rubber bushings on the axle either. It's free to scoot sideways there as it sees fit.

In addition, the way swaybars work they hardly make any change to the harshness of the ssupension. When going over small bumps the spring rate is barely changed at all. It's only when a side is compressed further that the sway bar starts adding its spring rate to that of the spring.
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I'm JohnMc, and I approved this message.