Oh yeah, I don’t know how common it is, but when manipulating graphs, if there’s a topo order, I seem to strongly prefer visualising things with that order respected on the page (vertically or horizontally). So your images committed a few minor crimes according to that aesthetic. I can also imagine that some other aesthetics would strongly prefer writing things the way you did though, e.g. with M←X→N. (My preference would put M and N slightly lower, as you did with the M, Xi graph.)
Oh yeah, I don’t know how common it is, but when manipulating graphs, if there’s a topo order, I seem to strongly prefer visualising things with that order respected on the page (vertically or horizontally). So your images committed a few minor crimes according to that aesthetic. I can also imagine that some other aesthetics would strongly prefer writing things the way you did though, e.g. with M←X→N. (My preference would put M and N slightly lower, as you did with the M, Xi graph.)