The Dillon is certainly capable of producing some very consistent and accurate ammo but part of my answer would hinge on what you consider a large quantity of ammo, how often you would load a batch and how much you will use different powders, charges, seating bepths and bullets. The Dillon shines at loading a lot of one load of ammo in a short time. It can be a PITA for throwing a few cartridges worth of powder for each of several charges, trying different seating depths or trying different bullets.
A O-frame or C-frame press is a handy thing for load development or small batches. I usually prep and prime a one to two hundred cases at a time so all I have to do is drop powder charges and seat bullets while working up loads or for small 20-50 round batches of hunting ammo. That is, however, based on my having milk crates about 3/4 full of once fired GI match brass in both .308 and 30-06 and a lot of brass that has only a few loadings on it.
My experience has been that even with a 550 or similar press a single stage press is a time saver for some things.
Lance