Within the Eldar community there is a love hate relationship with guardians. Many love using them others won’t even buy the models. Personally I love the little guys, they way I picture them is having the same armor and weaponry as everyone else except they’re just not as skilled at using them.
It’s like the scene in 300 where the Spartans meet up with their allies from the surrounding provinces. The Spartans allies were farmers, bakers, and candle stick makers, where as the Spartans were bread for war. Both groups had swords, armor and shields but one group knew how to use the weapons better then the other. So that’s how one could account for this idea that Craftworlds give their citizens crappy armor and weapons, it’s really not that, they’re just not as skilled as the aspect warriors. A guardian may not duck, dodge or dive at the right moment as a howling banshee might and a guardian may not know proper breathing techniques as a dire avenger would when shooting long range.
Now some people may mention well they have thousands of years to train and should be better skilled with defense and use of their weapons, true but they are just artisans. My argument would be that they’ve live for so long but what we consider as basic training done in a few weeks an Eldar could take years to complete something they would regard as basic training. Of course these are just thoughts I have and my attempts to explain how I see the guardians.