The big assumption here is that you want your profiles to expand in both directions, and equally at that. To achieve a profile that is not vertically symmetrical (such as straight or an “undercut”), you’ll need a different method. I can visualize how to do it, and it’s close to your method but it requires expanding each layer separately, then breaking the expanded stroke apart, discarding the one you don’t want, and expanding the resulting “half expansion” on its own. Adjusting the offset for each step will yield almost any profile you want.
It’s a lot more hands on, so I’d work with the end design’s symmetry. For example, if it has radial symmetry with 8 lobes, I would work with an 8th of the design, then copy/clone and rotate them into place so I can see what’s happening overall and work on the main repeating base.
Once I was happy with the end result, I’d unclone and join the 8 copies. Manual node manipulation like this is not always fun, but it would save you so much time here.