Gameplay mechanics should evolve. Lore should stay the same. D&D monsters/races are part of Angband lore and history. They are part of the game world.
Recently there was a post on reddit, wanna quote my tiny reply there:
There is big difference between 'gameplay' and 'lore' changes. Gameplay changes could make game better, rebalancing the game, implementing new interesting gameplay mechanics.
But the thing in current Angband changes is: lore 'sweeping'. Maintainer decided to remove DnD influence from Angband's lore, making it closer to pure-Tolkien - without kobolds, dark elves, Medusa etc. For 30 years it was mixed universe, people get used to it and they love it. No one asked to make such changes - it's not balance/gameplay, but lore changes.
As Xainiax said in reddit topic:
Lore is almost impossible to change in any fictional setting, people like what they know about a world to continue to be true.
Why not just create Angband 2? Leave vanilla as it is and create 'new' game, with new lore. Because after this major lore changes it looks like a new game to me. Like Moria vs Angband.
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