Shulker boxes are similar to chests and i think they can lag if you have a ton of them laying around

The performance hit comes from the way a block renders. Chests and shulker boxes are dynamically rendered every frame. They need it that way for smooth animations. Hoppers and barrels are static, they only get updated when they (or blocks in proximity) change.
Also there's a difference between shulker boxes and chests: opening shulker boxes increases their collision box to 1.5 blocks. But the performance gain is probably worth the mismatch between actual and apparent size when you are using shulker boxes in your main storage.