Abnormals Core adds hooks for Quark's flags, one would need to consult their team as to why that is preferred over using Quark's flags directly.
That said, I too have no clue what Quark's vertical slabs would do for this mod... would the OP mind elaborating on the issue?

checker block now has vertical slabs. No need for abnormalis core or anything of the sort

how?

I'm not a coder, but I bet that you need to make the vertical variant of certain blocks and code it so they are only available when Quark is installed

define "certain blocks". I would only think of the checker block since that's the only normal block which also has a slab in the mod

Pretty sure you'd need to have Abnormals Core as a dependency to do that (or make your own 'DIY quark vertical slab' system which would probably be a lot of work)

Pretty sure you'd need to have Abnormals Core as a dependency to do that (or make your own 'DIY quark vertical slab' system which would probably be a lot of work)

but vertical slabs are a Quark feature, and Quark doesn't need Abnormals Core to work