With that in mind, I was surprised that your test case showed any improvement at all --- it looks like the arrays aren't getting compressed for some reason.
You are right, it seems that they were not getting compressed, probably because the arrays were "seq 10000" which seems to not get compressed by pglz. When I changed the test data to an array containing 10000 ones, there were no speed improvement anymore.
I'll look into how to improve the compressed case and other issues you raised.