Flushing has very little to do with the end result. Proper curing DOES!
I can get very close to the same yield of hydro in my soil grows. It took lots of time to dial that in, but it works.
My organic water only soil grows cost less then any hydro runs I have ever done. Hydro runs do finish faster!
I get better taste from soil then hydro. Hands down.
If you manage each properly, you will get no real difference in potency that would cause you to do one style over another!
Lighting, as in nm range manipulation, has the greatest effect on potency over any type of chemical manipulation. Again, this is true for either style of grow.
The simplest lighting solution for this is to run MH till the week before the "flip". Change over to HPS for 4 - 5 weeks and back to the MH and run till done. (During those last weeks of bloom under the MH. Run the MH bare [in an open wing reflector] or with the glass removed from your air cooled hood to get the "extra" UVB blocked by the borosilicate glass.
Run this side by side with the "conventionally accepted" lighting method and you will get the point!