I'm strongly in favor of giving the parliament the ability to propose laws (directives). Currently only the comission can do that.
The way it seems to work in practice (here at least) is most partisan/normative legislation goes through the lower house upwards
And bipartisan (or broadly unpopular or highly technical) legislation goes from the upper house down
It’s more complicated than that, but a one way flow committee sounds extremely restrictive for meaningful reform
A small number of pathways is a good thing, one lone process is probably not (you risk over fitting on both sides)
Edit: Australian legislation has a lot of flaws, but this multimodal setup from my experience is not one of them
A common currency without a common fiscal policy has already proven not to work well.
The Treaties haven't changed since 2011 or so, and I don't expect any changes in the next decade at the very least.