Well, to the people that are complaining about Skellebro lackluster performances ...
First, remember how he started ... as Lv 0 grunt with very limited inteligence and strength, when even other skeletons were a threat ( actually a plot point ages ago ). While the author gave him oportunites to increase his skills ( some of them VERY contrived, TBH ), the issue is that he is still leagues away of the strongest people around, something the encounter with Madame and the ghosts showed pretty well. That is not to say he is weak nowadays, like his fight with the Apostole fragment showed ... just not at top league levels .
Second, and as even the MC complains about in this chapter batch we had, while he got increases of insight skill, the fact is that his inteligence can't be boosted by absortion and that he, after all, is still a skeleton with skeleton level inteligence and initiative ... in other words, a creature with enough inteligence to understand and act upon instructions, but not much more. That alone explains why he is so passive at times ... he, as a skeleton, was not made to take snap decisions or high intelectual prowesses and, predictably, fails miserably when forced to.
That said ... yeah, it is infuriating at times his passiveness and lack of awareness. But atleast it makes sense in universe: after all , he is a uplifted skeleton ( until proof otherwise ) and expecting much of him in terms of high intelectual abilities or good judgement is not a good idea.