There will always be a bias towards singers (or at least will be overrepresented) because, let's face it, it's Simon's best chance of making money beyond the show.
The golden buzzer gimmick doesn't bother me so much, because it's exactly that, a gimmick. Something to add a bit of "drama" to the audition stages. It's not as if the acts that get them wouldn't have got through. Even David's comedy acts, and I use the word "comedy" very lightly, would likely get through to make up the numbers/to make it easier for the better/preferred acts to get through.