Well, that's pretty much it. If Neo Arcadia a century or two later couldn't get a copy of X to work right, then I don't see how 21XX scientists could pull it off.
I remember the hilarious 'Light is the biggest [dark hold] ever' stuff, but seriously. Doctor Wily's Zero outlived X, technically, but then Neo Arcadia was apparently able to replicate a weaker version of his original body that was still, with Zero's true soul and intent powering it, fully capable of taking down Omega/the original. X? No one ever even tried to directly copy his design like the Black Zero copy and copy body in the Zero series, all the Reploids were merely based off his design and yet it took being completely and utterly immobile for his body to finally be destroyed for real. Even then, his soul was powerful enough to continue on until he finally decided to rest after exhausting himself.
One could argue that as of the Zero series, the Reploids were finally able to be human-like enough that technically X's special factors weren't so unique anymore, and that only expanded in the ZX series to the point of Humans and Reploids being blurred. Yet singlehandedly, Doctor Light was still able to create the machine that not only inspired all of them, but lived only second-as-long to his best friend and still had a farther-reaching effect overall on the entire history of the world.
I know i'm just reiterating a lot of things we've gone over a million times before, but it took over two-hundred bloody years for anyone to finally begin properly moving on beyond replicating the past and actually advance Reploid technology in a meaningful and nonretarded way (COPY CHIPS). Colonel and Iris are certainly not exempt from trying to create the ultimate soldier via compassion and potential, much like X; it was practically asking to fail in that regard, judging by this series' standards, even if Repliforce never went AWOL.
Doctor Light is practically the forgotten God of robotics.