Hard to beat a small, slick bottomed, fully locked 4x4 with the capacity to carry 1,000 lbs of payload when it comes to spraying weeds in the areas I find myself in.
The only items I could dream up to make this a more productive/versatile machine would be;
a) If it didn't have to ride on a trailer
b) More water capacity
c) Slow speed cruise control
The small trucks make a ton of sense.
Now if we could just get the manufacturers to start offering "trays" (flatbeds) like they do in Australia and get rid of the stupid truck bed entirely....