Micah Sweet
Level Up & OSR Enthusiast
See, I feel your stance is, "if the player wants something, just give it to them". I don't think its fair to the DM to just do whatever the player wants.Sure, but if the world had sea elves, and the player want to play a triton, why not accommodate the player and replace sea elves with tritons?. By your own admission, you feel that the races occupy the same niche.
Also, I choose tritons as an example for a reason: the argument had been made that many races was unrealistic because the would compete among each other and wipe each other out. This argument does not apply to tritons who occupy a different niche than most humanoids.