Do you remember RuneScape? You're right, I now have an Completionist Cape on my account in RuneScape. This means RuneScape gold I've successfully completed the game. Does that mean it's real? Did you actually kill the toughest boss? If you haven't killed all the bosses in RuneScape then how have you done it?
RuneScape is a primarily combat-based game. This is undisputed. The official RuneScape manual that I got from the 2006 scholastic fair explains this. The bosses play an important part in combat, therefore I believe it is fair that the Completionist Cape requires taking on all of them and destroying the entire group. Yakamaru will be a lovely dog, but I am a fan.
The team bosses are the issue. There is no guarantee you'll find a team. It's impossible to be "complete" and that can't be guaranteed. In terms of abilities, this would have been viable prior to the release of raids. There are now tradeable abilities. The idea of having all these as a requirement is similar to having each RuneScape weapon as an option.
While it was previously possible the Transfigure/Sacrifice, Transfigure and Devotion were removed from the two bosses. I'm not sure how I feel about this. If you didn't see it and are interested in more reading or discussion, I've added more to my last post.
It's a lot easier than fishing however, it's not as relaxing and enjoyable as Fletching or Cooking. They're not as difficult to train as the former two. Although Fishing isn't terribly difficult, I find it more frustrating more than Woodcutting. I had 99 WC in 2007 or 2006 - doing an assortment of Yews, Willows and Maples generally and buy 2007 runescape gold from what I remember it wasn't all that bad.