A fact can be part of some context, so there’s no issue there. The issue with answer E is that the conclusion isn’t trying to defend artistic preferences of people in general. It’s making a claim about artistic preferences. Super subtle, I know.
There is a group 2 indicator (only) and a group 4 indicator (cannot) in that sentence. So you can use either one, but generally it's easier to use group 4 indicators as negations and use the other one as the logical indicator.
From my understanding, words like "maybe", "should", "could" aren't conditional indicator words so they aren't diagrammed. Words like "are," "is," "must" and "only" can be diagrammed.
Similarly, "not both" can be used in a way that be applied to just about any type of game whether it be sequencing or grouping in nature, so context is very important.
The first sentence is just context and does not have a place in our conditional chain. You are correct that the quantifier ELCI should "some" over to LCI. So replace ELCI --> LCI with ELCI -some-> LCI. Still ac(A) is correct. Nice spot!