Diablo 3 is a travesty, it can't be fixed. Game mechanics isn't only issue.
Blizzard, in order to make their games even more appealing to children aged 5-12, created new universe which is very much like Marvel's. Mishmash of Diablo, Warcraft, Starcraft and now this new thing called Overwatch. Those worlds aren't compatible. Diablo is (was) dark and mature world, for people who prefer horror games. Warcraft is a fairy tale like Star Wars, despite the fact it stems from brutal Warhammer universe. Starcraft is similar but it is darker in nature and very sci-fi. They don't mix well. But they don't give a fuck. Money talks. Therefore they make games with all major characters from their games and pretty much destroy those characters in the process (have you seen those childish Diablo skins or King Leoric in Heroes of the Storm?)
They don't respect their lore anymore, they transformed into Activision's puppy. Luckily for us, they haven't reach final form because Activision still doesn't allow them. The moment Infinity bullshit universe fails among children, they will start producing interactive Blizzard toys/avatars. But Infinity cow still gives milk so we are safe for some time.
Just because Blizzard has transformed into something not even mom can love doesn't make Path of Exile an epic action RPG experience. It might be best of the crop atm, but that doesn't mean it is great game. Just that other suck more.