I have spent about 20 min just going through the someone's single claim my boat. In total I saw 4 very big claims. I believe the basic purpose of claim is protect your stuff, so you can track down the thief if something was stolen.
Since the map is very limited I suggest one of the following workarounds to do something to claim size:
1) the costs per tile increases exponentially after 10k (for ex.) tiles claimed.
2) make amount of tiles claimed per one character limited.
If you really want to claim all the world, you still have a possibility to do this using village claim