Consider this:
If you are sanding a car and trying to get a smooth surface.....you start with course paper, you end up with smoothness relative and corresponding to the size of the grit.....visible scratches remain but course grit cuts fast so you start with that.
So then you progress to a finer and finer paper, until your scratches from the grit becomes invisible unless you have a magnifier....then you polish to get a mirror finish.....you can't take short cuts. Oh you can start with fine paper, but you'd be sanding for months to smooth the undulations from scrapers and rasps....or longer.
Now, what if you mix the grits and make paper that has both 600 grit particles and 2500 grit particles in it......it would sand faster than 2500, (but not as fast as pure 600)......and it can only be as smooth as 600 since you are going to scratch the finish with the bigger particles.
In the same way, Walnut is course, corncob is fine. Mixing them together only slows down the Walnut, and prevents the higher polish of pure Corncob.
Bottom line: If you don't have time to polish with corncob all day.....and don't mind the semi-gloss finish of Walnut...then using pure Walnut is faster than mixed. If you want higher gloss use pure corncob and be patient....or get a wet tumbler and stainless steel pins.
Before I bought my Thumlers and pins, I used pure corncob only. I started a batch in my garage early in the morning before I go to work......it tumbles all day....@ 5 or 6pm I turn it off and have really polished brass.....just not in the primer pockets or inside the cases.
Wet tumbling gives me the same thing in 3 hours....inside and out and pockets too. Do I need that? Just mentally, emotionally
But I never cared for walnut with its outside only clean, and never the sight for sore eyes bling.....need speed?....move up to wet tumbling.