"Frivolous" is a silly way to discuss the investigatory system, especially if the framing is unsubstantiated = frivolous. It's like the term "government waste" - it's only waste because you don't like the purpose of the spending. It's only "frivolous" because you don't like going through the process.
If you want to create a system where a senior will never have to endure an investigation that is ultimately unsubstantiated, you've created a system that has no realistic avenue for juniors to report discrimination, abuse, etc. Personally, if I'm going to err to one side, I'd prefer it be the one where juniors have a system to identify problems, and I'll eat the risk of enduring an unfounded investigation.