I have had the exact same problem as you, but with different software. I have done a couple of projects where I did some graphics in AE and then exported to Premiere. When I exported to Microsoft DV from AE, the text looks quite pixellated, as you described.
Exporting to a lossless codec from AE and letting premiere do the DV conversion solved the problem. So I don’t know if AE just doesn’t render DV well, or if I am missing a setting in AE, or what, but I always export lossless from AE, then let premiere do the DV rendering.
If somebody has a better solution that would be great because this has been bugging me forever as well.