It is the tournament and the current champion is in it. The winner of this GP will be the real champion. K-1 has Kyotaro as HW champion, but who cares? K-1 World GP 2010 champion is the ultimate fighter in the world of kickboxing because Kyotaro was participating. Who can possibly suggest that Kyotaro is better than Overeem just because he has the belt and Alistair don't? The same could be said about Schilt, but it is slightly another story based on the fact that he is already 4-time GP champion, so it's not that clear... and another thing is, the tournament takes place in one day, I mean the most important bouts, so injuries is indeed a factor. Now, Strikeforce's tournament will last almost the entire year, so the winner will become the best fighter of the organization in the eyes of everyone, especially when you think that Alistair got the belt by beating Buentello and Rogers 2+ years later.
I agree that winning the GP is the most important thing in K-1. Alistair is ranked higher by everyone thanks to his win in the tournament. It's weird to see Kyotaro defend his belt the next time though, seeing as he lost to the monster Semmy in the GP and now lost to Mousasi under K-1 rules as well.
The winner of the tournament in Strikeforce is going to be the number one heavyweight fighter in SF without a doubt. Whether it's Barnett or not.