Could using heavier gloves hurt performance in my case?

the problem with using 10oz gloves when you train is the tendency for you to wear your hands and wrists out faster due to the lack of cushioning, especially on the heavy bag. as far as sparring goes, wearing the heavier gloves is usually due to you wanting to protect yourself and your partner from receiving too much damage in sparring. the problem is there will definitely be some degree of adjustment when you use the lighter gloves in an actual match.