The triangle from full guard is so easy to deny but when there's lag or just when the action is going fast and there a lot of quick transitions then that's when you see the triangle transition get completed before your fighter ever even does the animation.
But overall the triangle is a pretty easy sub to deny. Try denying the kimura from full guard with a old tv and that's harder. That's the reason I went out and found the lowest input tv out there. I needed rubber guard and that dumb kimura ppl spam "yes I do too. lol" blocked from ppl doing it over and over to me. Now I deny even with the lowest rated fighters in the game. Rubber guard and triangles are easy denials with my eyes closed.