I love triangle choke and use it as my main submission.
But frankly, it can become way more difficult to make it work against bigger & stronger opponents if you do it from the guard.
You could say similar things about armbar from the guard, especially in no-gi.
Even if you have fantastic triangle/armbar skills, applying these submissions from the guard to larger opponents requires a greater degree of precision.
In other words, it can be easier to escape from these submissions when you are on the receiving end.
You should still learn and work on them, but it’s also good to know what submissions are generally difficult to escape from.
One of the most difficult submissions to escape from is d’arce choke.
It’s a variation of arm-triangle choke (you triangle your opponent using your arms instead of your legs).
When it’s fully locked, it’s almost like a game-over move. The reason why it’s so hard to escape from d’arce is because the d’arcer would be controlling the opponent’s neck and arm in such a way that the strangled opponent cannot move their arm or get rid of the d’arcer.
For example, you can set up d’arce from the side control top, the mount, the knee cut pass, the turtle, and the front headlock position.
As far as your positioning is concerned, you typically need to be in a dominant position to set up d’arce, but the great news is that you can use d’arce to get to such a dominant position, too, when you use it while passing your opponent’s guard.
If you have short arms, d’arce may not be for you, but otherwise, it’s worth learning d’arce and adding it to your submission options.