"In all Cases affecting Ambassadors, other public Ministers and Consuls, and those in which a State shall be Party, the supreme Court shall have original Jurisdiction. In all the other Cases before mentioned, the supreme Court shall have appellate Jurisdiction, both as to Law and Fact, with such Exceptions, and under such Regulations as the Congress shall make."
You’re right, it is plain English. There are two sentences in the section dealing with the Court’s jurisdiction. The “Exclusion Clause” is a clause of the second sentence, modifying the second sentence, which deals with appellate jurisdiction. The first sentence, dealing with original jurisdiction, has no such clause. It’s plain English grammar: a clause in a sentence modifies that sentence.
Do you really want Congress to have the authority to strip the courts of jurisdiction over cases involving states as parties? Do you not realize how much that would expand Fedeal power over the states?