For casual level play it’s indeed fine. But the “flatness” of a level doesn’t really mean much. You want to know which specific part of a nearby room someone is in. To the left… in front? Behind? Are they going through the hallway or cellar in cs_italy?
Like any game, you get huge value out of slight advantages when you get to the more high level skill.
I was around CAL-M level in 1.6 and I never had a surround sound setup, but I'm unconvinced that it has any meaningful benefit over headphones, which worked perfectly fine for intuiting where someone was. That's hardly a real benefit in higher level play, anyway because you know where everyone could be, anyway, and your movement is dictated by that knowledge as well.
Like any game, you get huge value out of slight advantages when you get to the more high level skill.