Imagine how many fewer problems they would have with their enemies if their stuff all worked, and they had more of it.

IIRC that actually did happen a couple of times in that universe. The answers were usually "A Machine God eats the factory planet" and "Necrons". So, the outcome was... not good.

On the other hand, the T'au have a pretty good handle on their tech, and they're improving it all the time, so maybe the humans could take some lessons from them. On the third hand (*), the T'au as a whole seem to be immune to Chaos corruption, which is a luxury that the humans do not enjoy.

(*) Or tail or tentacle or what have you.