The great thing about brewing: There's no "wrong" way to do it.
The awful thing about brewing: There's no "wrong" way to do it.
Do people use 30min additions to make good beer? Sure. There are lots of ways to make good beer. Is the beer good because of the 30min hop addition? I doubt it. In a blind tasting between a beer with a 30min and a 20min hop addition, all other things equal, I doubt most people could tell the difference.
I think you should pick a method that works for you and stick to it so you can get consistent results.