You are not the first man to think that way. Some people already did what you'r talking about and released proper seeds.
A lot of bullshit breeders and a market full of seed producers instead of breeder doesn't mean that there isn't good stuff going around. Working with next generation weed is overall better, but you need to know what to work with.
Why go back to landraces when people already went a few generations ahead like you intend to do? Just need to choose the properly bred stuff, not backcrossed or selfed genetics (like "OG Kush" or "Bubba Kush") but polyhybrids can prove to be very rewarding
Stabilizing your own polyhybrids takes a long time, specially if you want to have up to par results with current breeding efforts.
I believe that in order to find truly elite cuts you need a large genetic pool and a very large selection - not the kind of stuff you usually get with landraces.
By having high variability in the offsprings you can choose the very very best cuts and breed with them.