It might be the "high-level hub" but what's so special about Prifddinas that it deserves an entire set of Completionist Cape requirements that make up one of the most important requirements outside of the quest cape, all tasks RS Gold, and 2595 total? These are just my thoughts.

Did you ever play RuneScape before? It's true, I now own the Completionist Cape for RuneScape. This means that I've finished this game! What do you think? Did you kill the most difficult boss? If I didn't kill all bosses in RuneScape How do you know if you've finished the game?

The combat system in RuneScape is extremely important. The official RuneScape Handbook I bought at the Scholastic Book Fair states so. And bosses are a big role in combat and, in my opinion, it seems fair that taking the entire group on and beating them all be a prerequisite to obtain the Completionist Cape. Yakamaru will be a wonderful dog, but I am a fan.

The team bosses are the issue. It isn't a assure yourself that you'll find a team. It is not possible to be "complete" and that can't be guaranteed. This was feasible prior until the release of raids. But now there are tradeable abilities Buy OSRS Accounts, and having them all as a requirement is like having every weapon in RuneScape as a requirement.