You are mostly correct. An ammendment, once ratified, cannot be "removed", but a new ammendment can be introduced that "undoes" a previous ammendment. For example, the 18th ammenment, ratified in 1919, abolished liquor in the entire country. The 21st ammendment, ratified in 1933, reversed the 18th ammendment.
What ammendments might be made in the future can be a fascinating discussion, especially when conducted among intelligent people with open, but realistic minds.
Where I think there could be some meaningful changes today would be in the area of terms of service for various elected officials. I think it would benefit the country if the presidential term was limited to one 6 year term with the understanding that the person could run again to be re-elected after someone else had served after him or her. In other words someone could be president two or even three terms, but never two in a row. this would allow a president to learn the job, and then devote 5 plus years to doing the job without having to worry about getting re-elected. We would get a lot more out of the president that way. The other change I would suggest is with regards to the terms of congress. They have to be re-elected every other year. Think about that. A new person gets elected. It takes them the better part of a year to even learn the job. Then they spend the second year running for re-election. They do that every other year, so basically, we get one year of work out of every two years a congressman or woman is in elected office. Change theirs to the same 6 years as the senators, we would be way better off.