I mean It's already been 5 years since RDR, I'm pretty sure it's closer than you think. Even more so when you take into consideration the fact that they publicly stated that the Red Dead series is now considered as a tentpole franchise by them. Honestly, I feel like it's taken that much time in the first place solely because they were (are still?) banking so much with GTAV, and are now taking their sweet time with the finishing touches.