Parakeetman
No one wants a throne you've been sitting on!
I think that for "Monster Hunter clones" people also refer to such titles with a heavy local co-op mode, exactly as Phantasy Star Portable. The fact that this game was able to sell over 600k is a clear indicator that tried to attract Monster Hunter fanbase, and succeeded i it, given that the series never topped such numbers.
Phantasy Star in general has always had a fanbase before hand. So the fact that it went portable and lots of people had a PSP, its no wonder why it sold.