I like to brag about small groups
I do have one of the larger ovens and it is pretty nice. FWIW, lead has a very low conductivity so it takes a while for the whole bullet to reach temp. The good part is, for powder coating, only the surface temp of the bullet matters. A more consistent temp in the oven is more important, which is why I got the convection oven.
But, I am not a 'batch' person. All of my bullets are stood on their bases and separated on the baking sheet with good air space around each one. If you do baskets of bullets you need to monitor the temp of the center of the basket of bullets. A thermocouple is needed for this. A convection oven might help getting the batch up to temp faster.
Do you 'need' a convection oven? No. I baked thousands of bullets with my cheap toaster oven and they did just as good as the ones from my convection oven.
The REALLY important part is the temp in the oven. The thermostats on the ovens are notorious for being wrong. My expensive digital oven is off quite a bit. I bake at an indicated 370F. The measured temp inside the oven is 400F. My older, cheap, well used, not digital oven was exactly correct. Set the dial at 400F and the measured temp was 400F. And, as I stated above, baskets of bullets need temperature measurement at the center of the batch.