I have the centramatic on 4 rigs. 3 have 35" rubber the other is in 19.5's.....I never balance tires and they runout round as can be all the way to the end....even cheap mud tires.
6 years is that balance point if look at average miles driven per year. 10K miles year is 60K at 6 years. The belts should be in good shape at that point and the tires shouldn't have started dry rotting yet unless you're in the desert. YMMV literally
I've had probably 10 sets of used tires over the last 15 years.. At some point though, just buy new tires