I mostly shoot aluminum and wood arrows out of my trad bows, and I think aluminum is easier to tune that carbon. Aluminum shafts are available in a bunch of different shaft diameters and wall thicknesses, typically giving you multiple options for a given bow-- for example, a 2114 shaft and a 2016 shaft are both considered "500 spine" (I believe there's a little difference in the deflection number, but they're both considered 500 spine). However, the 2114 is a little lighter in weight. Both aluminum and wood shaft's spine are fairly sensitive to changes in shaft length and point weight, so you can make small adjustments in point weight and/or shaft length to adjust arrow flight.
That being said, proponents of carbon shafts would probably say that carbon is easier to tune, since carbon shafts have a higher dynamic spine range than wood or aluminum. So, any particular carbon shaft (say, a Gold Tip 3555 shaft) should be able to be tuned to work for a wider range of bows (draw-weight range) than a particular aluminum shaft (say, a 2016 xx75 shaft). I believe that most carbon shafts are less sensitive to point weight changes than aluminum or wood. Based on what I've read in some other posts, I think the spine of a carbon shaft is more sensitive to shaft length changes than point weight changes (although both do matter).
I guess it depends on what you mean by "easier to tune". Guys who like aluminum or wood probably think these are easier to tune because they can make small adjustments in point weight and/or shaft length and see differences in flight characteristics. Some guys who like carbon might say that carbon is easier to tune because the shafts are less "finicky" (wider dynamic spine range)-- if you've selected the shaft that works best for your bow (say, 3555 vs. 5575), leave it long, stick a heavy point up front (whatever point weight you need to get your total arrow weight where you want it to be), and see how they fly. If too weak, go with a lighter point. If too stiff, shorten the shaft a little bit at a time until you get the flight you want.
Just my 2 cents-- I could be wrong. I shoot them all-- wood, aluminum, and carbon (although I have much less experience with carbon).