It's good to have an output chain you can rely on. I don't know what I'd do without a sub, doesn't mean the next guy needs one. It's all about finding a chain that works for you, but don't be fooled into only classifying things labeled as "monitors" as a solution.
Most cheap monitor setups can aguably(meaning opinion tends to stray both ways, but enough that it's always a debate)be outperformed by speakers in the same pricerange, and once you get to a pricerange where that statement isn't true...things start being referred to as both "speakers" and "monitors" depending on the consumer.
Examples include Dynaudios, JBLs, Yamahas...once you get past the "8" monitors" you get into a field where things don't need such classifications to boost egos.
So don't think KRK RP5s are any more "accurate" than Polk, Sony, or Yamaha 5" Bookshelves hooked to a halfway decent amp.