I think that for us, the issue is too much clay and it impedes the growth of the bulbs. We have gotten maybe one or two that were baseball size, but other than that, just golf ball sized. While those size are good for cooking for two, it is still disappointing because we used to get them nearly softball sized when I was a kid in Northwest NE.
I'll amend more this year. I thought I'd done a decent job of loosening things up with sheep and peat, compost and the tiller, but it's pretty stiff already this year.
I'd be OK with even golf ball sized onions, because like you said, you can use them for cooking. At the rate mine grow, I might as well use the bag of onion sets and call it good. Save the effort.
My mom grew softball sized red onions in her garden in Colorado and I don't remember her doing anything different, but it's been a while ago.