That is correct. Since we talk about lower then Gb speeds
It’s all twisted pairs as any other CAT cable. You probably just had a shitty quality cable.
Yes, but the CAT does not simply do nothing, shielding is probably the most distinguished factor on the CAT rating and it increases the signal integrity and therefore the max speed you can push across the cable. Saying “all just twisted pair” is just BS, or just try to get 10 Gb speeds on a CAT 5 on 100m long cable.