Hey @Annaerith, The other thread looked too busy, so I thought I would answer your questions in here.
Not exactly, Spells are generally more favorable than all gem/skull matches, although that is broken down by how effective each spell step is perceived. As mentioned in the other post, the AI scans the current troops and board (Side Note: It does NOT know what is going to be dropped in from outside the current board) and circumstantially picks what it thinks the best move is (with some randomness added in there).
But that being said, moving the slider too much to the right will start to override some spells.
Mostly correct. Changing the sliders can change the priority of spells directly relating to the gem colors, but not to as much of a degree. This means that changing the Red gem priority would not guarantee a Red colored troop to be cast over a Blue colored troop as an example. The aim of the gem priorities is more to change how the AI plays the board more than the spells, as many of the examples given of “Predictable AI” involved the board (e.g. skull baiting), so the priorities allowed players to try and get their defense teams to avoid some of these player traps from occurring (or keeping the AI a bit more unpredictable compared to the PC+Mobile/old Console AI system).