Disagree with your first statement halfway, agree with the second.
The 14th incorporates itself to the States by its own terms, not by court decisions, and also all the articles of the Bill of Rights via the "Rights and Immunities" clause.
And I agree with you that posting the Mosaic law on a courthouse lawn as a memorial doesn't rise to "establishment" in the sense the Framers meant it.
If the Judge planned to post the Commandments, and then refer to them when ruling on motions or handing down sentences, then that would be "establishment", in the same sense that Islamic republics establish Sharia.
Were its authors aware of its secret anti-religious meaning?