If I had a nickel for every time I saw someone wearing platelegs while casting magic spells, I’d be rich.
Not everyone knows the best in slot gear to use when training. It’s important to familiarize yourself with what is the best in slot equipment for whichever task you’re completing to be the more efficient you possibly can be and in the long run, save a lot of time.
Being a 1 defence pure basically also means that no armor will help protect you. Iron armor is extremely weak and any enemy will have a high probability to inflict damage on a pure every hit. As a range pure, it's better to focus on what makes you more accurate rather than what defends you better since the defence is almost irrelevant.