"35mm" doesn't have better bokeh than "6x7". What 35mm lens and what 6x7 lens? A triplet is going to have a lot jitterier bokeh than a double-gauss type no matter the format size.
Generally speaking though the bigger the format the shallower the depth of field for a given field of view. This is because of the focal length - a 90mm lens is a 90mm lens no matter how you slice it. You can stick that 90mm on a 35mm camera and it will be a long lens (different from being a telephoto!), or if your lens covers 4x5 then it will be a wide angle at that format. A P67 105mm f/2.4 is going to have the same depth of field (approximately) as a Nikkor 105/2.5 if you were to shoot them head to head on 35mm - it just has the capability to cover a larger format. Now, if you were to get an equivalent lens on 6x7 - say a 200mm - then for an equivalent f-stop (f/4 on the 105mm, f/4 on the 200mm) there will be shallower depth of field in comparison, because the focal length is longer.
The most succinct way to put this is that bigger formats require longer focal lengths for an equivalent field-of-view, and longer focal lengths have shallower depth of field - period.
And remember - these cameras were used by professionals in their day, pretty much any of them is good enough for amateur work.