The "FPS-problem"

Well
it is fact that the most ps2 games will run on this emu, but at least there will be one problem too.
Most of the games run with an realy low fps-rate that means the games won't be fully playable.
My question is, if someone will create an better graphik-plugin, will this make the game run faster ? or will it take more than a "simple" plugin to play games like on ps2 ?
Where the hack is the problem ?
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Excuse my bad language