A good potato salad should be a marriage of discernible, toothsome chunks of potato in a creamy, starchy dressing. Rather than adding globs of mayo, sour cream, or tahini, the key to that balance of textures lies in using two different types of potatoes.
By using both waxy potatoes and something starchy like a Russet, you get those firm tater chunks that keep their shape, along with the mashed potato-esque qualities of a fluffy Russet.
As the Russet loses its form, it mixes with your dressing, adding substance and starch and helping it cling to the waxier guys.
There's no need to obliterate the Russets; chopping them into cubes and mixing them with the rest of the potatoes will be enough agitation to help them crumble just enough.
I like a ratio or one medium Russet for every 450g of new potatoes, but feel free to play around with it to suit your potato salad needs.