The main thing I love from elems and kit-engis is their ability to access any of their skills on demand. You are on fire and need water $5? You can just attune to water and access it instantly.
Weaver sacrifices this, as well as their #3, for very little added value.
When I hear dual element, I think being able to attune main hand and off hand separately. The issue with that is that it would take 8 buttons to attune (1 for each element, x2 because main hand and off hand). My suggestion is to add a 5th slot after earth that simply toggle which hand the attuning affects. Kind of like the upkeep abilities of revenant, you can toggle it between main hand and off hand. So if you're in main hand mode and attune to water, it will be only the first three skills that would change to water, with #4 and #5 unchanged.
If you want to change the off hand attunement, you toggle the attuning hand and change element. This way, you keep flexibility for a limited complexity increase (I'd even say it's simpler than having to attune twice to access #4 and #5 of a given element and having to plan in advance).
What do you think about that?