While I understand your gripes with the straight lines, and sometimes frustrating world gen.
I fail to see the issue with the multiple fields, the only field that seems out of place here is the one the trader is on. All the other look natural and create interesting intersection of multiple rock types.
The straight lines in this screenshot are very localised to the bottom centre of the screenshot, and most of them aren't perfectly straight, making it seem more like nitpicking than pointing out poor/faulty generation.
Generally speaking I do agree it is possible to come across large straight lines in gravel/sand biomes, but most of the ones I saw where small straight lines that were 'acceptable', keeping in mind that sometimes 'better/perfect is the enemy of good'. Especially with generating worlds, adding more layers to the generation can ruin it further, or be much more cost intensive which would be another problem, or work out, but it's tough to know what the result would be without investing time.
I do think that during world gen, rock strata should overlap and not be distinct biomes, creating regions of mixed rock/gravel/sand. It might fix the problem of straight lines and I feel it would be more 'natural' to see biomes blend with each other rather than have distinct boundaries.