That's the key to me. When LLs are long, or just constantly full, those are the times when standby is brought to a STANDSTILL to catch up with the LL. That leads to 60+ minute waits on a high capacity attraction like Haunted Mansion. It's those peak LL ratios. They're frustrating to everyone.
Disney can also increase G+ slots per hour, making that service more valuable and usable with more inventory.
I would expect wait times to change noticeably if DAS #s (which was maybe 60% of riders at some attractions, remember) were reduced by some significant amount. And I think that's going to make a difference to other guests, both with and without G+.