I think that there is a lot of guilt over this -- having a nice run and providing for the birds with a lot of enrichment vs. giving the birds free range.
If you have only a few bantam birds, then if you can get purchase or borrow an EX-pen or two, you could set up a temporary area for an field trip on grass once a month that your birds may enjoy.
My birds spend most of their life in their run and I do not feel bad about it, because their safety is one of my responsibilities. Nor do I feel bad if I provide them with food based enrichment -- that is exactly what free ranging is, and I do not believe that anything should eat the same thing day in and day out.
What I do is I try to make sure that I permit at least an evening a month that I allow the girls an evening out, about two hours before sunset, in which I sit outside with them. They get to explore, I get to watch them (and determine which weeds they currently like, which makes it easier for me when I am pulling things for them later), and they are looking to get back into the run after filling their crops.
I do not kill my birds when they stop producing; they live out their life with me and I do what I can to make their life enjoyable.
I currently have a six month old puppy. He thinks that he should be able to run free. But I trust neither him nor the rest of the world (as he looks very much like a fox, and I know people's attitudes towards foxes), so despite what he "wants," he isn't permitted to run free and I am guilt free about that.
You are doing a great job!