the WG was relentlessly targetting nico robin merely for her knowledge of the ancient language.
but they never showed any motivation for chasing luffy unrelated to the piracy, D clan affiliation and being the son of dragon.
and the way they talked about luffy's fruit makes it seem like it's the ultimate threat to their organization, which logically means that they should've sent armies just to secure it.
we know the WG have knowledge, power and unlimited resources, and they are not lazy nor stupid, so the only explanation for this mess is not the WG incompetence but rather oda's bad writing.
this is just oda destroyed his own story with a ridiculous retcon and pure large scale PIS..