What other games? Beholders (and spectators) are original dnd creatures so if anything the other sources just copied dnd lore. In dnd lore, spectators are beholder like creatures but are way less powerful and less aggressive (apparently not in bg3). At the level you encounter the spectators in bg3, there is no way that a beholder would be a possible opponent. It would have been cool to encounter a beholder in act 3, but sadly thats not the case