The secret is they are better than you
You obviously came back, a month or two after other players who play our game daily and are now super pro on this version. Tough buiscuts, keep playing and gain your expertise back to their level with time. One tip is single headshots ARENT always enough to kill an opponent, depends on the weapon.
shotgun = without armor
magnum = without armor
silver pp7 = without armor
You get the idea, armor on your opponents may be rendering only a portion of damage needed even with power weapons because they had armor and you possibly didn't
Thats the only variable.
The game is the most stable ever and implying elsewise is foolish. Maybe you used to compensate
too much with your aim, for ping/hitbox detection in other versions (I did). Aim closer to the head if you used to really compensate for valve coding, because killermonkey keeps cleaning the netcode meaning our game is uber refined.