Center alignment for last nodes in a tree layout diagram

I’ve tried to play with the options in the tree layout,
and have a layout with nodes that looks like this (modified screenshot)…

…but what I would like is for the nodes at the bottom to be “centered”. Yet playing with the options, this does not seem to work. I notice in the flowchart example, the “loc” settings are all customized to achieve a similar type of layout. Is resorting to “loc” the only way to achieve such a layout (if so, not viable for my set of circumstances).

That is not a tree-structured graph, so it should not be surprising that it does not behave the way that you want in all circumstances.

You could use LayeredDigraphLayout. Or if the graphs are suitable, you could customize TreeLayout, as demonstrated in Parallel Layout.