To be clear, there are plenty of virus vaccines that are lifelong.
It is unfortunate that the covid mutates as fast as influenza, but it was not a given at the beginning of the pandemic. Many scientists claimed that enveloped viruses were less likely to mutate, and that the covid vaccine would likely maintain immunizing effectiveness for years.
It was a disappointing outcome, not an obvious one.
Antibodies are not long term, ever. They always degrade in the blood system.
...but that's also not the only type of immune response that a vaccine generates.
Vaccines cause the creation of b-cells, which retain the memory of this virus antigen and will re-create antibodies if the virus infects the host.
b-cell immunity is persistent - for years, and probably decades. But because it is very hard to measure (it resides in your bone marrow), it is therefor not often reported on.
Having said that, it is hard to imagine that a 4th booster significantly increases the number of anti-covid b-cells - let alone ones that can impart immunity against the newer variants.
Your comment does not address the contradiction in the parent comment.
The contradiction is that two media outlets are stating opposite statements from the same source with regards to whether the 4th booster raises the amount of antibodies.
The rapid tests are still quite useful because a positive test is very reliable and saves you several days of waiting for PCR results.
Perhaps the test results should be labeled "Yes, you have covid", and "meh, not sure".