DR in anime track does have meaning, it gives it depth and direction, without it 5.1 or 7.1 would've been all over anime encodes which is even way worse than stereo since it bloats up filesize like theres no tomorrow.
edit: on second thought, a completely flat DR would make a "whisper" and a "shout" sound the same, plus irrelevant bgm would pretty much overpower speech or other sounds since they're equally loud.