If you’re going to do direct arm training, you need to make sure your technique is actually targeting the muscles in your arms. Tricep pushdowns are a commonly butchered exercise. They get sloppy quick, taking the tension away from the muscles and placing it on the elbows and shoulders instead.
I see a lot of guys at the gym try to use too much weight for pushdowns and they compensate by integrating a lot of movement at the hips and torso.
If you actually want to hit the triceps, you have to work the triceps. Not the hips, or abs, or shoulders. You have to tighten up the movements and set your ego aside. The best way I’ve found to tighten up the tricep pushdown is to drop down to the kneeling position and use a longer rope.
The reason this works so well is that the kneeling position forces your torso angle to remain the same throughout the move. Because your torso isn’t moving all the tension through the range of motion and especially at the bottom is placed on the triceps. This means gains. You’ll probably have to drop the weight a little, but that’s because you’re actually targeting the triceps instead of simply abdominal crunching the weight down.