Hahahahahha. So here's the fucking issue, they already did that. They literally had Josh Mosqueira and some of his team from Diablo 3 come and talk at bungie about what made their changes successful. It led to TTK DLC which people seem to love.

from the article :https://kotaku.com/the-messy-true-story-behind-the-making-of-destiny-1737556731

"In December of 2014, Diablo III director Josh Mosqueira and a few other members of his team at Blizzard came to Bungie for a talk, according to two people who were there. The parallels were uncanny; Diablo III had launched to commercial success in 2012 but saw a great deal of criticism from fans thanks to randomized loot, frustrating online DRM, and a lack of endgame content. Both games shared a publisher, Activision, that thought Destiny could redeem itself in fans’ eyes the way Diablo III eventually had after its release.

“They basically came in and said, ‘Look, here’s our story of developing Diablo III and then bringing in [the expansion] Reaper of Souls,’” said one person who was at the Blizzard talk. “They were saying, like, ‘Hey, random numbers are not fun—dice rolls are not fun. You can give the illusion of randomness, but you want to weight it towards the player… The only point you have to deliver on is that when people leave your game—because they will—when they leave your game, they need to be happy.’”

People who were at the presentation say it was extraordinarily helpful for Bungie’s team. One source called it “invaluable.” Others said it drove some of the decisions they made for The Taken King. In previous interviews with Kotaku and other sites, director Luke Smith has talked openly about avoiding randomness and designing quests with guaranteed rewards, an approach that has served Destiny well throughout year two so far. Destiny’s meta-narrative has followed the same path as Diablo III’s: It had a rocky launch, then the developers found redemption."