Queen Beryl's story begins before the Sailor Moon saga that we know. Before the scope of the story (although we are told about it), she helps Metalia crushthe Moon Kingdom, killing Serenity, Endymion, the Senshi and indirectly Queen Serenity. Metalia is sealed away by Queen Serenity but we are left assume that Queen Beryl was killed and reincarnated at the same time as the senshi or else her story does not make sense. It is Queen Beryl who reawakens Queen Metalia kick starting the Sailor Moon saga.
Beryl's role as a villain is strong because of her vehement hatred towards the Moon kingdom. This makes her irredemable as a character meaning that we all root exclusively for the senshi as they set about defeating her. This is unlike future villains who have deeper reasons for what they do and are thus more rounded and challenging characters. Queen Beryl's simplicity is a vital fragment of the story at this stage for two reasons. First is that Usagi and the senshi are still coming to terms with themselves and their new found powers, to expose them to a complex and deep version of Beryl would have thrown their character development off mark somewhat. Second is the fact that the Senshi are the main characters of the story. It is essential that the audience side with and love them before they begin to perform challenging or morally difficult behaviour or else there is a risk of dispersing or even losing the viewers.
"Why must you always take everything away from me, Princess?" - Queen Beryl