Generally speaking, item level is a decent indicator of an item’s strength, but will never be the only important value on an item. Every spec scales differently with stats and different stats will have (sometimes) wildly different value - and that may even change around depending on how much of every stat you have.
Taking elemental shaman for example, it looks like Mastery is much worse than the other stats and you’d want to balance out Crit, Haste and Versatility while almost completely avoiding Mastery. That alone might cause an item with Mastery to be worse than another item of lower item level without Mastery.
With your recommendations for example, you’re losing Mastery and Haste, while getting some Intellect, Crit (more than directly visible because of an additional 5x31, i.e. 155, from the third corruption effect) and Versatility.
While that is a downgrade by item level, you’re also getting better Azerite traits on your chest, as you’re using at least one enhancement only trait in your current chest. You’ve also set enhancement as a higher priority than elemental (see the order of specs to the left), so you’re telling AMR not to change anything used by that spec. Thus it’s better to use a lower item level piece with appropriate traits.
The other items are also switching around some corruption effects and using one additional item with corruption. Corruption effects can be really strong and (depending on the exact effect and your current stats) can be stronger than a high amount of basic stats - although those effects will be removed completely in a couple weeks when the Shadowlands Pre-Patch hits.