I tend to space tomato plants closely. However I had one plant last year germinate in a row with extra shallow topsoil with a higher clay content. It had tons of room but germination was understandably poor in that area. The plant was barely growing.
I decided to add a bag of potting soil, organic fertilizer, and sand around it. Boy did it take off. I pulled it up at the end of the year to see and it sure had a lot of root growth into the new substrates.
So there is definitely a component of my growing that is very limited by my natural soil, especially in the areas where the soil is visibly paler. I think I've added sand enough to know it's effective. Organic matter, compost, peat is definitely effective. Double digging and adding a lot of the above into the clay accumulation layer would probably result in very different tomato plants from the same seed.
One phenomena in my garden, if you let water run long enough it starts to flow through the topsoil. You can see it come back out further down slope.
In the early spring when I get my vernal pool some years I think that's what happens. The melt water moves though the topsoil, doesn't absorb into the subsoil, and then accumulates into the vernal pool which takes a very long time to drain. I think if I dig some deeper trenches and amend that water might stay put.