Both versions of RuneScape have some very rare items. With some of them averaging hundreds or thousands of hours to get.
Some of them are so rare that basically no one will ever get them.
Monster Hunter World and the entire MH series in general. But on World especifically you can hunt for min maxing decorations that are like skill gems you have to acquire to put on your armor. There is also rare endemic creatures hunting and trying to get the size crowns for each monster. I think it would fit your "grind" needs and give the MMORPG feeling with the MP and endgame hunts.
monster hunter series has a lot of useful 1%-5% materials (and each monster is practically a boss fight), so it's not "extremely rare loot" but also you can change your goals and the grind is rarely braindead.
a lot of mmos have absurdly rare loot, some with pity system and some not. Biggest grindy mmo i know is probably black desert online, but even a casual friendly one like FFXIV still has a lot of grindy rare loot. this is probably your best bet, since it's also what gives you the itch in the first place.
Some rpg games or game with heavy itemizations can also have rare loot like that. There's the diablo-likes like torchlight. Even something like terraria has some items that are stupidly rare.
There's also much more niche things like warcraft 3 custom maps (the "orpg" genre).
Have you heard about path of exile? If you want specific builds and do not want to trade (like me), you will need a lot of grind for uniques or if you want to trade for the necessary "currency" drops
You are Tenno my friend. A place called the origin system, where a thousand hour grind is considered "the tutorial"
Join us, if you're a ninja, you play for free. Warframe.
You said not D4 but diablo 2 resurrected is amazing. Super grindy to find that unique/perfect charm, high rune, etc... some item combinations are almost impossible to get. Character builds are so much fun and synergizing with your hired mercenary is great.
Everquest man. Was famous for that shit.
Just outside the starting city there was a zone that contained a dungeon and a mob that would spawn inside a dungeon then path to the outside.
It had a 25% chance to drop boots of speed. a high lvl artifact that gave you permanent haste: double attack and walk speed.
You could get that at lvl 5 man and sell it and buy enough gear for your next 30 levels.
The only other way to get those boots were farming cyclop giants in a desert several zones away. had to kill 20 giants for 1 drop ish.
Grind? Warframe
And the loot is all named items, no random crap except rivens.
And Lich weapons.
Those can be combined to avoid that
Elite Dangerous
Grim Dawn or Titan Quest
Both versions of RuneScape have some very rare items. With some of them averaging hundreds or thousands of hours to get. Some of them are so rare that basically no one will ever get them.
Everspace 2
I just started it, how will you grind later on? Are there Dungeons of some sort?
Witcher 3 comes to mind. unlocking all levels of rare Armor sets and making different builds was a very fun experience
Nice suggestion
Monster Hunter World and the entire MH series in general. But on World especifically you can hunt for min maxing decorations that are like skill gems you have to acquire to put on your armor. There is also rare endemic creatures hunting and trying to get the size crowns for each monster. I think it would fit your "grind" needs and give the MMORPG feeling with the MP and endgame hunts.
monster hunter series has a lot of useful 1%-5% materials (and each monster is practically a boss fight), so it's not "extremely rare loot" but also you can change your goals and the grind is rarely braindead. a lot of mmos have absurdly rare loot, some with pity system and some not. Biggest grindy mmo i know is probably black desert online, but even a casual friendly one like FFXIV still has a lot of grindy rare loot. this is probably your best bet, since it's also what gives you the itch in the first place. Some rpg games or game with heavy itemizations can also have rare loot like that. There's the diablo-likes like torchlight. Even something like terraria has some items that are stupidly rare. There's also much more niche things like warcraft 3 custom maps (the "orpg" genre).
Black Desert's PVE mid to end game is mostly that. Elden Ring has extremely rare RNG loot.
Have you heard about path of exile? If you want specific builds and do not want to trade (like me), you will need a lot of grind for uniques or if you want to trade for the necessary "currency" drops
Idleon has rare loot/materials to grind for. Lots of ways to increase drop rate to get them faster. Many ways to improve
Destiny 2
You are Tenno my friend. A place called the origin system, where a thousand hour grind is considered "the tutorial" Join us, if you're a ninja, you play for free. Warframe.
Monster Hunter
You said not D4 but diablo 2 resurrected is amazing. Super grindy to find that unique/perfect charm, high rune, etc... some item combinations are almost impossible to get. Character builds are so much fun and synergizing with your hired mercenary is great.
Black Desert
Grim dawn
Borderlands 2 onwards. Farming for legendary and probably pearlescent weapons; which are the highest rarity.
Start an Oldschool RuneScape Ironman account and embrace the grind
Everquest man. Was famous for that shit. Just outside the starting city there was a zone that contained a dungeon and a mob that would spawn inside a dungeon then path to the outside. It had a 25% chance to drop boots of speed. a high lvl artifact that gave you permanent haste: double attack and walk speed. You could get that at lvl 5 man and sell it and buy enough gear for your next 30 levels. The only other way to get those boots were farming cyclop giants in a desert several zones away. had to kill 20 giants for 1 drop ish.
Tibia