"Comments go out of date quickly" is true -- it's the "there's no point in investing in them" that's incorrect. In addition to being valuable in the short term (to both you and anyone else who ends up looking at the code), "comment just became outdated" is a highly valuable signal that a prior assumption made by other code could now be false, and you should look into that.
I have worked on teams where the code is very well documented (basically every public method, parameter, property or class gets a comment) and it's not at all hard to keep up to date. Sometimes people forget, but when you look at a PR and see the usage or meaning has changed with no corresponding comment change, it's easy to flag.
