If you want something to create/intercept/edit/tamper/replay requests, this is your tool. If you want to script any of those things, this is still your tool.
However, burp comes with a lot of bells and whistles that don't make a lot of sense to build in to mitmproxy, but you can script yourself. For example, there is no intruder, spider, or scanner tool. But, they have an easy to use interface to write scripts that will be run on every request you make, or individual requests.
Or, you can just pass all mitmproxy traffic out to burp and get the best of both worlds.
Still if you're comparing the free version of burp with mitmproxy they do seem very similar. I wouldn't know for sure since I've never used mitmproxy.
For software developers doing routine integration-test security checks, I think there's probably a lot of value in the scanner. For professional testers, though, I think the scanner does more harm than good: if it's routinely spotting things you don't spot manually, you should revise your technique.
I don't think pathoc/pathos are really close to what the Burp "Intruder" fuzzer does (and I'm not in love with Intruder either). A lot of people also rely on Burp's spider, for which there's no mitmproxy analog. Obviously, there's Burp's scanner, but I think scanners are a bad idea and wouldn't count this against mitmproxy.
Have you achieved any good results with the intruder? if yes, an example would be awesome. (Personally I have never used Burp)