This is true. We can repeal any amendment we like. But your theory on what types of amendments may be ratified or not is nonsense. Here is the actual law:
The Congress, whenever two thirds of both houses shall deem it necessary, shall propose amendments to this Constitution, or, on the application of the legislatures of two thirds of the several states, shall call a convention for proposing amendments, which, in either case, shall be valid to all intents and purposes, as part of this Constitution, when ratified by the legislatures of three fourths of the several states, or by conventions in three fourths thereof, as the one or the other mode of ratification may be proposed by the Congress; provided that no amendment which may be made prior to the year one thousand eight hundred and eight shall in any manner affect the first and fourth clauses in the ninth section of the first article; and that no state, without its consent, shall be deprived of its equal suffrage in the Senate.
If you look at Article One, Section 9, you find that the first clause refers to the importation of slaves, and the taxation of said slaves:
The migration or importation of such persons as any of the states now existing shall think proper to admit, shall not be prohibited by the Congress prior to the year one thousand eight hundred and eight, but a tax or duty may be imposed on such importation, not exceeding ten dollars for each person.
The fourth clause reads:
No capitation, or other direct, tax shall be laid, unless in proportion to the census or enumeration herein before directed to be taken.
So there it is. If common sense doesn't work on you, maybe plain English will. Right there it says that prior to the year one thousand eight hundred and eight no amendment could affect the clauses named. There are two obvious conclusions which can be derived from this language, both of which refute your notions:
1. That after 1808, the people had the expressed right to pass amendments which would directlt affect the clause regarding direct taxes.
2. That implicit in this language is the recognition that outside of those specific, limited items in Article 5, any amendment could affect any part of the Constitution.