Unfortunately after some tests there is not a mode that I can see producing this kind of geometry automatically. In some cases such as in the image below you can use the Vertical Top/Vertical Bottom options. You can find out more about this in our stairs
However if you need to retain circular shapes there is no obvious solution that will allow you to combine vertical or stepped and adaptive modes.
The only for now I can see to remove the unwanted deformation is to create geometry that is designed to compensate for the effects of using vertical deform mode. To do this you would need to counter-deform the balustrade segments so that when they are distorted by the vertical mode at a specified stair angle they appear correctly. Like a real staircase, this will have to be done manually for the specific angle of the staircase you are creating. Here's a simple example (Also attached):
To create these segments you can rotate the geometry anticlockwise the angle of you staircase. Next reset the XForm and apply a FFD2X2 modifier. Skew the right side downwards until the horizontal elements are once again in alignment (If the style starts at the top of the top of the stairs you may need to do the mirror of this):
If, as in your attached file, you have a flat landing area you will need to use a conditional operator and material IDs to ensure you use undistorted segments for the flat landing sections and distorted segments for the stairs. You'll also need to amend the padding and you may find you need to slightly adjust the segment's height.
I hope that's of some help, if we find a better solution I'll post it here. meanwhile if you have further questions, please let me know.