We use a nightly build and test environment with TestComplete. The ProjectSuite test run takes 12h and has a huge test result tree. It is pretty complex to compare the actual ProjectSuite test resu...
Certainly QAC integration could be included at some point or yes it could indeed solely be a feature of QAC. However, it would definitely be great to have in TC where you could simply select two test runs from the log and go "Show me the differences".
Perhaps QAC would allow for more detailed reports or trending reports.
FYI here's an example of the Netsparker reports I'm talking about. Scroll down mid-way through this page to "Comparison Reporting" or here's a screenshot. Instead of security vulnerability related entries each row might be a TC test or group of tests. Each column would be a test run.
https://www.netsparker.com/blog/releases/announcing-netsparker-21/