The Atom processors reportedly struggled to run 2D games on Namco's System 2 hardware like Assault, often dipping well below 100%
For reference on a 4Ghz i7 Assault runs at 1600% most of the time, dipping to 1100% in places in a regular 64-bit build.
There are many, many 2d games that run slower than Assault.
You get what you pay for....those processors were designed for low power, low heat output, not performance (it looks like, at the same Mhz rating an i7 has roughly 6-7x the single core performance of the Atom)