If you're happy with your agent's performance using surface level o11y to track down issues then that's fine. This is what pretty much the entire industry is doing and it does usually work! QA focuses on root causes because it can look through the app's entire execution and provide evidence so your agent doesn't need to guess when figuring out what the fix is. That guesswork is what we're trying to eliminate, for when the surface level stuff doesn't clearly point at the problem.
It boils down to "other products find the issue and leave the root cause + fix to your agent, our product finds the issue + root cause and leaves the fix to your agent".
Who says I want your agent to root cause? Other products already give me the repro steps, video, trace, network logs, etc, and my agent is in a much better position in terms of context and setup to find the root cause and proper fix.