You sound like you’re one of the players who don’t appreciate a properly crafted RPG experience with an actual ending. Unlike Diablo III, a proper ARPG game must have an arc and pacing that makes sense. Diablo III is the definition of linear: you do one thing in order to do the next thing - hello bigger GR number. Do you know why you feel like Diablo III has an endgame? Because there’s no fleshed out beginning or middle game. The game itself starts at the end level so nothing else really matters. Smart design. 
Diablo II’s endgame was checking out battle.net after your singleplayer completion. Diablo II’s endgame was running through the game in nightmare mode and finding new items to trade, pvp or pve with. Diablo II’s endgame was Hell mode with more amazing item types and possibilities 
. Diablo II’s endgame was making a different TYPE of the same archetype from the ground up, not just swapping skills as if they’re completely separate from the character like a modern shooter load-out. Diablo II’s endgame was running hell cows and helping the SEVEN other players in the game. Diablo II’s endgame was magic finding bosses and special monsters from each act. Diablo II’s endgame was hardcore duels with loot up for grabs. Diablo II’s endgame was player-created iron man matches. Diablo II’s endgame was Uber events. Diablo II’s endgame was hunting players with bounties on their heads 
. Diablo II’s endgame was racing the ladder. Diablo II’s endgame was trading. Diablo II’s endgame was crafting the high end gear. Diablo II’s endgame was rushing players for a fee (hellforge?). Diablo II’s endgame was amazing player-created MODs. Diablo II’s endgame was not based on a final level or accompanying infinite leveling system to give us the illusion of never-ending content, it was incorporated throughout the game to give you a NON-LINEAR experience.
Oh, and if Diablo II was devoid of trading? Half of the list loses its appeal or goes out the window. Trading can amplify or improve other parts of the game that might otherwise not be as thrilling.
In your almighty, expert opinion. 
