The MITM proxy feature is comparable to Charles, mitmproxy and others. Typically, in software like OWASP ZAP, Burp Suite (and now Hetty) the MITM proxy is only part of a larger set of features for doing research. E.g. the proxy is used initially for discovery of endpoints, and then the results are used for manual/automated requests/attacks on a service. Hetty doesn't have these features yet, but OWASP ZAP and Burp Proxy do.