Namco and Taito were a little bit lazy in playing to the PCE's strengths, graphic fidelity being one of them. You have to forgive Namco a little bit, though, as their system 2 arcade hardware (Splatterhouse, Dragon Saber, Ordyne, Bravoman...) had 8 bit-per-pixel (256-colour) graphic tiles, when most other hardware at the time (PCE, Genesis, SNES, Neo-Geo, CPS-1, Sega Arcade units) used 4bpp (16-colour) tiles. They're obviously unportably lush.