"Just do heavy shrugs and deadlift to build traps." Sure, that works for people with short clavicles, short necks, and narrow shoulders. They can do some deadlifts and some ultra heavy shrugs and their traps grow immediately. But those on Team No-Traps often have broader shoulders and longer clavicles, making it much more difficult to build traps.
Instead of going super heavy on shrugs and jumping around with the weights like you're having a seizure, contract at the top of the shrug for three seconds. The shrug doesn't have a long range of motion. It's short, and going ultra heavy means doing fewer reps. This may be why heavy shrugs don't work for a lot of lifters. There's not enough time under tension.
Do these with dumbbells and seated using a cambered bar for 4 sets of 12. With a three-second pause at the top of each rep, this makes for a long, painful set with plenty of time under tension. Don't sweat the weight as much as making the contraction as painful as possible.