This was a project for the PSP only (although it has been ported since to PS2), and so were designed for maximum output for a 482x272 screen, whilst staying within polygon and texture budgets relevant to the platform.
Bosses were 2500 tris, small characters were 1500- 2000 tri depending on whether they needed to talk. Weights were one influence per vert, with two influences used sparingly. Textures were small and 4 bit.