Whenever I make a large bonfire I normally use leather work gloves while I'm tending the fire with my fire rake or if I have to move a partially burning log by hand (within reason of course). I've been looking at the aramid fibers that you can buy that can resist up to 932°F (500°C). Would those be better for fire tending than the heavy leather work gloves? Is there a downside to them being synthetic?
If leather gloves are doing the job, why change?
There are a lot of variables, but it really comes down to exposure. For the most part gloves only protect your hands. When working in and around a large fire, you also need to consider exposure to the rest of your body as well.
Increasing the fire rating of you gloves, only adds value if you also increase the fire rating of things that are protecting the rest of your body.
When wearing standard leather work goves, in my experience 98% of the time it is heat on my face, arms and legs that drive me back from whatever work I am doing in large fire management. When heat in the hands is the issue, it is probably time to back up anyhow. The only time I have ever been burned wearing leather gloves is when hot embers found their way into the glove from the cuff. If this is a problem for you, get leather gloves with a cotton or nomex cuffs.
IMPORTANT NOTE. If any part of gloves, lining, cuffs, etc are fabric it is extremely important that you ensure the cloth is not synthetic and/or is fire rated. Synthetic fabrics melting and fuse to skin is a real risk with extremely unpleasant impacts.