What if the High Lords decided say "what if", then take all the deadliest Catachan Fighters, put some gene-seed in them, not tell tell all that Space Marine doctrine bullshit, and just let them do their thing?
How stupid or awesome would that be?
Oh yeah, they get Flecktarn camo color schemes.
What about taking kids from Catachan? How is it not a recruitment world?
Well, I suppose there are things Catachans can do that a space marine really couldn't. Catachans can go stealth, while Space Marines, even at their stealthiest, are for shock and awe.
Because those from Catachan are all Rambo thanks to decades of living on a death world. While Children are probably a bit better, there likely aren't the sheer numbers needed for recruitment.
And there are quite a few stealthier space marine chapters that can do stealth just fine.
I think Catachans get that good because they grow up as normal humans.
Early geneseed implantations would basically make the scouts playing with cheat codes and they will never git gud like other catachans
For a logical reason, Catachan Fighters have such a level of genetic drift to adapt to their homeworld that that they are considered to be near abhuman, hence the nickname "mini ogryns", this would be problematic as space marine geneseed must be implanted in someone who is genetically viable, which is normally baseline humans or those with deviations endemic to the chapter's existing recruiting worlds. Psykers are a different can of worms entirely. So unless the geneseed is slightly tailored for Catachans there would likely be an above average rate of possibly fatal implant rejection. This wastes both good geneseed and good potential guardsmen on something that is almost redundant.