Flicker filter (and softening) should be turned off regardless. They're legacy settings for use with CRTs. Those only serve to degrade image quality on a modern display.
Are you sure your games are actually outputting 480p? What region are they? Many European titles only output in interlaced. NTSC (particularly North American NTSC) is preferable.
Also, what aspect ratio is your display versus your output. If you play a widescreen (16:9) game at 480p, it's not going to be as sharp as a standard (4:3) display at 480p, because you're using the same number of pixels to cover a wider area (essentially, the pixels are being stretched horizontally, into rectangles, via a scaling factor).
Burnout 3 looks just fine for me. Again, this is one of the few games that supports anamorphic widescreen, so, if you're outputting a widescreen image, the overall picture won't be as sharp as a standard 4:3 output, though it will fill the entirety of a 16:9 display.
I don't believe Phantom Dust supports widescreen, so your choice is limited to 4:3 480p. It also looks just fine for me.
Panzer Dragoon is a bit of an oddball. For one, it's one of the early SEGA games that doesn't play nicely with v1.6 Xboxes (which is a separate issue). Additionally, I don't think it actually outputs 480p. It's like 3XXp or something. You'll have to check on that one, but it, in fact, does not look very sharp for me (though that's simply due to it's nature).