I mean Orks were originally Krorks, beings superior in every aspect to for example human marine primarchs, who were desigend to take on not only the galactic spanning might of Necrontyr but even the C'tan. But since Old Ones were really callous and cruel beings, they didn't given a shit about them and they degenerated to Orks as we know them (there's a lot of plot shield in this too but it's irrelevant atm). Orks are also more of an organic von Neuman machines.

Oh and speaking about Old Ones, the worst thing in the universe is what they did to Eldar. Old Ones were masters of the warp, they did know more than anyone about it. Yet they still designed Eldar as beings with not only good talent for warp, that would be not bad by itself, but also as beings with incredibly strong emotions and emotional feedbacks, which left them extremely vulnerable to warp - all that while knowing how warp works and by themselves being largely immune to this adverse effects due to their own nature.