Diablo 4 is already a completely different beast
Because of all the backlash, Blizzard has Diablo IV Gold had to come out and assure players that the upcoming Diablo 4 won't be anything like Diablo Immortal. That may be true, but the inclusion of cosmetic microtransactions in the next Diablo installment does mean players are a little wary.
The launch of Diablo Immortal is still recent, and Diablo 4 is at least several months away, so the criticism and skepticism feel very fresh. Diablo 2: Resurrected may have been largely able to overcome its less than ideal launch, but Blizzard hasn't really been in gamers' good books lately.
Diablo 4 is already a completely different beast from the ill-fated Diablo Immortal, as it's a full-priced game designed solely for PC and consoles. There will be multiplayer elements and PvP encounters, and although Diablo 4 will have a large open world for players to explore, it is not an MMO.
These aspects alone should distance it enough from Diablo Immortal, but players do sometimes have long memories for developer mistakes. As long as Blizzard is more transparent with features and any paid elements than it was with Diablo Immortal, it should be able to win players back to some extent.
Diablo 2: Resurrected isn't as reviled as Diablo 4 Gold buy Immortal, but it didn't really represent a step forward for the franchise. It was a fun hit of nostalgia for long-time players, but it didn't necessarily entice new ones.