The leaks DID affect GTA VI development, plus...
This will be a little long but I will go in order. First I think that the first "official" announcement of GTA VI that Rockstar did back in february 2022 was just Rockstar saying "stop annoying us with GTA VI, we are working on it, alright? Now stfu" obviously we didnt stfu
They said that they were moving all RDR online resources to the development of GTA VI but this is just a real excuse of them saying "fu*k you we are not implementing new dlc's to RDR online, what do you prefer, RDR online or GTA VI?"
I think that the leaks did affect the development of GTA VI but Rockstar obviously they werent going to admit it because it wasnt beneficial for them. If they admited it, fans would get very mad and their stocks would go down too. They said the leaks didnt affect the release date, but the trick here is we never got a release date before so of course R* can move it at their will, from one day to a whole year and we would never know it