Why the systems are necessary? Easy.
The game is EASY. Challenge and difficulty increase the longevity of a game. Take Dark Souls - the game itself is probably 10 hours, but due to the challenge, it takes most people 70-80 hours to beat on their first playthrough.
Classic could get away with simplicity because it compensated with killing you for making a mistake. Ooh, you accidentally pulled an extra raptor in the barrens, die. Now walk to your corpse. Quests, especially back then, when the game was new, were challenging. You had to read the quest text, and reading, as we know takes time. Not all, but many classes fought enemies one. By. One. The game just took it’s time, so it didn’t need systems to keep you playing. You had to use bandages or food in order to recover. There was downtime. This was the main system of the old expansions.
Now… when you have a quest to kill x amount of enemies, you just pull all of them at once and slaughter them in 3 seconds. You use your self-heals to get yourself back up instantly, zero downtime. YOU GOTTA BE PRESSIN BUTTONS ALL OF THE TIME. But because the game isn’t taking its time anymore, it needs to find other ways to take your time. And this is where these systems come in.