Ok like so what's the difference between this and something like that Korean top down game whatsit called? Is it just the darker world? The blood? The demons?
Lost Ark is essentially just a Korean-style MMO from a top down perspective. It controls like an ARPG, but it's not really one in the same way that Diablo or Path of Exile or Grim Dawn is. Loot is mostly just pure stats with no modifiers (+int, +strength). Most gear that drops doesn't have new visuals to it. Most of the focus is on reaching endgame and then doing the raids, similar to other MMOs. I don't know if this will make sense, but in Lost Ark you progress your character so you can do higher tier raids. In Diablo it's the reverse, you do content so you can progress your character.
Diablo is mostly presented as a single player game but with a more connected world that supports grouping up and MMO aspects, but it's not the emphasis unlike Lost Ark. In Diablo you're getting lots of different gear with modifiers (+2 to X skill, dashing makes icicles pop up, etc.) and looks and have a lot of ability to customize your build. You can probably make any build work if you're clever about the stats you focus and what you invest skill points into.
So they both pull from the ARPG template, but with very different things they emphasize.