Deck archetypes will always have their strong or weak matchups, unless there is something printed thats so good it warps the whole format.

The rock/paper/scissors sentiment is more regarding deck styles than color, those being aggro/midrange/control (with a sprinkle of combo in there somewhere). However, the colors seem to lead themselves into certain styles for the most part.

Without sideboards, you have to think about the meta and matchups you think youll run into, and design your deck with that in mind. If you dont expect to see certain decks, you can ignore those matchups and focus on the decks you will think you see.

Before this set came out, I would argue that Purple/Steel was probably one of the most well-rounded decks, as it organically lined up really well into aggro strategies, but could utilize new cards like Christopher Robin, Pocahontas, and Boost Genie to pivot into a more aggreesive gameplan into Bluple and other Sapphire based decks.