Severe performance issues with large inventories

What I expected to happen was...:
Your inventory items would not meaningfully effect performance

What actually happened was...:
Increase in mspt of about 5x with a full inventory

Using a datapack to run a command for all players with a certain SelectedItem every tick increases the mspt even more, a datapack running it 27 times per tick is enough to crash the server with a single player

Steps to Reproduce:
Create a bundle, fill it with 64  unique items

Create a shulker box, fill it with 27 copies of the bundle

Fill your inventory with the shulker boxes

Also effects 1.17.1