Breeding seed, from crap bag seeds

I have heard more than once that if you want to make your own cultivar that one of the parents should be a pure landrace strain as this gives the strongest building block and you run into less problems like loss of vigor etc. Can anyone enlighten further? Is this why a majority of bag seed is crap genetic profile? I've heard too many xs that this didn't turn out like the bag it came from. Exceptions to this exist I know but is it true?

Bag seed can be great or shit...just depends on where it comes from

Get some good genetics and start with that

All you can say about bag seed is it’s a mystery, I’ve had good plants and Hermies from it.
It’s good for a practice run till you get your op dialed in

Idk about breeding w them bc I haven't ever done it. But I've grown some really nice plants from mystery bag seed...

Those 2 are from bag seed...

Who in hell saves a seed or seeds from shit weed? I’ve grown some damned good stuff from bagseed. But then we had to sit down and name it because people gotta have a name. Made the price go from $10@gram to $20 too.