Should my citation graph be acyclic?
If the two papers are already written and submitted at the same time, I don't see why not. You are right about the upsides: making information easier to find for the reader. This is one of the purposes of citations! The only small addition I would make is that you should submit a copy of B along with A (and the other way around), so the reviewers can evaluate the need for this citation (as they do with “regular” citations).

And to end on a practical note: this will probably no inflate your citation count anyway. You submit your two papers at a time, then let's say A is accepted before B. So A is published with a reference to “B: F. Poloni, submitted for publication”, which won't be counted in citation databases. Then when B comes out, it will feature a proper citation to A (either in full, or through DOI if A does not yet have full citation information), and this citation will be included in databases.