Why has it become so sweaty? netcode? hitreg?

Eh wouldn't say its due to players being sweaty. I see that term being used a lot by players that tend to lose and can't just accept that they are not as good as another player. Not saying that this applies to you, but just pointing out that the term might not be directly related to the issues you are mentioning. (e.g. How does the player that killed you a minute after you go into cover indicate that the player is a sweaty player? Don't see the connection.) What you describe sound more like registration/netcode issues.