Sorry if I am not understanding you but it sounds like you were wondering why DT scores weren't at the top of the leaderboards for maps and that DT plays were giving more PP than the top plays.
This is due to the fact that beyond just that for osu score does not equal PP is that the mod multiplier for DT in CTB is very low for really no reason. DT only gives a 1.06x multiplier despite usually (outside of some weird exception where HR gives more) gives the highest PP increase on the map. People still recognize DT plays as usually the most impressive scores even if they don't go to the top of the leaderboard and the PP system reflects that as well.