If your GPU has low usage, then you're very like CPU-bound. If you have a 60Hz display, you're also gaining nothing by not using vsync.
Just so you understand, in games like CS:GO vsync is nothing short of the devil. The added input delay is worse than anything you suffer through not using vsync. Also, when your frame rates are good you don't really have to worry about tearing. I played at 120hz and generally speaking my FPS is above 200, in 5v5 it's usually capped around 300 and it stays close to there most of the time. No tearing to speak of.
And OP, it does sound like you're throttling pretty hard. Generally speaking CS:GO is more reliant on your CPU because most players use lower graphics settings. So yes, you're usually CPU bound. But your GPU also shouldn't be at 80c when it's only at 30% load... something doesn't round right there.
First, I've play many, many games, including twitch shooters (which I'm quite good at). I always use vsync, and I never have any kind of display lag because of it, with the exception of the poorly done console port Dead Space.
Second, if you're not using vsync (or FreeSync, now), then you are getting tearing. The higher your frame rate, the more tearing you tend to get when playing a twitch game, which changes the view orientation quickly and frequently. That you don't notice it is not to say that it's not there, and that it wouldn't drive others to distraction.
I agree a GPU at 80C with low usage doesn't sound right.
yes, i have a 60hz monitor, but i feel like the tearing if game doesn't reach to 120fps, that's why i'm worried about unstable fps
yes, i'm using lowest graphics setting with AA
no, i have no idea what cause that throttle, cause another AAA work fine, can you guys give me some advice or solution?
//p.s.: im using launch options: -hight -threads 8
here's the picture i just took, thing even worst