A set of cards of a particular type with spell and trap cards to support that type works, yes. Where as a randomly gathered group of powerful cards, just for the sake of having powerful cards, is not. That being said, you're not limited to just 1 type. Many types go well together such as Spellcaster and Warrior, or Winged Beast and Dragon. With this type of deck, you'll likely have a particular card, or set of cards you're wanting to get out and use to control the flow of the duel.
Ninja's set revolves literally around his cards getting into play to negate his opponent's spell, trap, and monster cards, so it's not a grouping of random stuff. With a deck like this, you have more options of choosing different cards, but the theme of your deck needs to be explained to me.
Looks good to me. I like the E-Heroes, and actually did consider using them until I found my Harpie deck. ^.^