diagnostic is used on 190 questions. A few are about diagnostic software, a few are about some specific display of diagnostic information, a few are on questions asking how to troubleshoot a problem, and most simply decorate any type of question about a hardware or software problem.
troubleshooting is used on 1,092 questions. I didn't examine all of them, but this tag also seems to be decoration on questions about hardware or software problems.
The vast majority of our questions are about hardware or software problems, and diagnosing/troubleshooting is integral to answering most of them.
If product recommendations were on-topic, there might be use for a tag to associate with this function. Since they aren't, we would generally want a product-specific tag.
Some are used on questions about debugging code of some form. Most true code debugging questions are off-topic, but we generally allow ones for small chunks of code for VBA, batch files, or other on-topic subjects. In those cases, though, we expect the OP to show their work. So those "debugging" questions are just problem solving questions, and debugging is an integral part of the process.
These three tags (four including the synonym), don't seem to differentiate anything useful. Even if they did, they are prone to misuse and should be replaced in those cases with something less ambiguous.
Should these tags be eliminated?