Yes, that's a good observation. In actual pronunciation, there is in practice no difference between 'disgust' and 'discussed'.
That is because after the sound /s/, the distinction between the voiced/voiceless pairs like /d/ and /t/, /b/ and /p/, and /g/ and /k/ is neutralized. A voiceless consonant that follows /s/ loses aspiration, the 'h'-like puff that usually accompanies the voiceless
Following the unvoiced /s/, the /g/ of 'disgust' is frequently at least partly devoiced. 'Disgust' and 'discussed' can therefore sound very similar indeed.