We've been there before and we've been there before, or at least somewhere similar to it. When Diablo 3 launched in 2012 an auction house in real money that players could buy and sell their item drops. In theory, it was there to stop the fraud and Diablo 4 Gold cheating that plagued the trading of items with Diablo 2. However, to guide players toward that auctionhouse Blizzard reduced the drop rate of loot in the game to an level that the process of equipping your character with a weapon became a tedious chore and the game in general was boring to play. The auction house that was a snobbery was taken down and drop rate were increased in 2014 Diablo 3 instantly became more entertaining, even before changes of the Reaper of Souls expansion elevated the game to a classic level.
The lesson: It could be logical on paper for you to think about monetizing Diablo's loot. However, when you do you take all the fun out of the game. The same thing happens with Diablo Immortal and it's apparent before you get to the endgame because it's embedded into the game design. Loot drops aren't as impactful the character's progression is artificially controlled and distributed across too many systemsthat are grinding and too fine. It has been more artfully concealed than at the start in Diablo 3, but it's similar to a boring and boring game. A battle pass purchase or paying a huge sum for legendary crests won't do much since paying for the best item drops will never be as thrilling like just getting one.
I'm unsure if there is a way to isolate the core of what makes buy Diablo IV Gold enjoyable from the mechanics of free-to play commercialization. If there is, Blizzard and NetEase have not yet found it.