What is the purpose of the ink delivery disks found in most rollerball pens?
Your reasoning actually comes quite close.
I found a quote through Quora, credited to John Lienhard from the University of Houston after having contacted Pilot:

&quot;The trick is to keep just the right amount of ink in contact with the wick that feeds the delicate roller ball tip. The discs are baffles that balance the forces of surface tension against air flow resistance. Regardless of the angle, just the right amount of ink stays in contact with the wick.

The pen's &quot;containers need complex baffles that let surface tension position the liquids&quot;, which makes sure that &quot;the pen writes beautifully in any orientation.&quot;
In Pilot's words, as used to promote their pens on various commercial websites:

&quot;The V System ink regulator is a direct result of Pilot's fountain pen technology. If excess ink flows from the ink reservoir while writing, it is temporarily stored in the special pen core by capillary action. In that way, amount of ink flowing to the pen point always stays constant. This mechanism ensures that the ink supply remains stable to the last drop.&quot;

This disc-system is similar to those found on fountain pens, here called a &quot;finned ink buffering structure&quot;: