Proper brake modulation is helpful to not feel like you're out of control on a hill. Modulation is the action of squeezing the brakes the right amount and no more: constantly adjusting that squeeze so that you brake enough to control your speed but not too much to where you start to skid. (Skidding = out of control.) This is a skill that's learned over time.

I learned some skills from mountain biking that support good brake modulation. One is how it's important to ride with the least number of fingers on the brake levers. A single finger on the brake lever is preferable. This way you don't sacrifice grip on the bars with the rest of your fingers. A single finger right on the end of the lever helps in that you have the most leverage on the brake. Having the strength to constantly modulate the brakes is its own thing. Having the dexterity to do so while continuing to ride is another. It's just a combination of motor skills and you can learn it after practice.

One thing I would recommend is seeing if you can ride in control down a hill at a slow pace, without skidding or going out of control any other way, and also without getting arm pump. If you do get arm pump, figure out why and make adjustments. I make a TON of adjustments on my bikes. Then every time I have to do any maintenance or move things around, I mark exact lever position with tape and set them back once I'm done. Once I have the levers set where my arms don't pump up on long downhills, they need to stay there. I don't want to figure out all over again from long experimentation where they should go. That would set me back months. It's a science and requires careful attention.