That's not how it works. Instead of 1L of strong broad-spectrum herbicide you use 1L of strong narrow herbicide for weed A, 1L of strong narrow herbicide for w

That's not how it works. Instead of 1L of strong broad-spectrum herbicide you use 1L of strong narrow herbicide for weed A, 1L of strong narrow herbicide for weeds B & C, etc. None of the narrow herbicides are weak, they are just more specific in their target because you need something that kills the weeds dead but does not kill the plant you want to stick around and grow.