why is it that in a solution, the lesser solute dissolve fastest?

Answer 1

If the rates of solvation are comparable, the solute that is smaller in quantity would dissolve first. The same amount of the greater solute will also have dissolved by then, but some of it will still be left because there was more to begin with.

The rate of solvation is not always comparable, and it's entirely possible for a greater amount of one solute to dissolve faster than a smaller amount of a different solute that is less active. In particular, more highly polar substances dissolve more quickly in water. For example, table salt would dissolve more quickly in water than sugar would, even if there were initially slightly more salt than sugar.