"thus" is an important word in interpreting one of the founders meaning. You can argue that it's only his opinion that the establishment clause means that. But you can't argue that it was only his opinion that it should.The 1st Amendment states "Congress shall make no law respecting an establishment of religion; or prohibiting the free exercise thereof." It then states that Congress cannot abridge free speech, or the press, or the right to peaceably assemble and to petition the government for redress of grievances.
There IS NO "separation of church and state" listed in the Constitution--only that CONGRESS cannot establish a "national" religion like the Church of England had done. Our Founding Fathers were overwhelmingly Christian and wanted the freedom for everyone to practice their religion how they saw fit. The entire LIE about church and state separation was from a letter from Thomas Jefferson to the Danbury Baptist, where he stated his opinion that there should be a separation between them.
And if that is a founder's opinion of what the establishment clause means. It's reasonable to conclude that this bit about no separation between church and state is your opinion. It's only your opinion that it's a lie.
BTW, the first amendment is incorporated. So effectively the 1A applies to all levels government. Or do you think that a state can prohibit the presses? Can a county government ban all conservative speech?
You may not like that it's incorporated. But now that the 2A is incorporated, what do you think of it now? Should Illinois be able to confiscate every firearm, because the 2A only applies to the US congress?