I like Linuxbrew because I can install things without needing to mess with the system packages. I'm using it on my TrusNAS SCALE server to install things like fish and neovim. The stance of iXsystems has always been that TrueNAS is an appliance and you shouldn't touch the system packages, so I try not to apt install anything.
But, as said, for it to work you have to set up yet another package manager which will works against the systems package manager, leading to out of date packages and probably broken dependencies. Rust already has a working system that will put binaries to a standardized place that will properly integrate.
I know almost nothing about cargo since I don't do rust, but if it works as you say, integrating with the system's packages, you are more likely to end up with broken dependencies.
Brew keeps it's packages separate, so breaking is less likely.
No, it won't. When rust "installs" an application, it will compile it as described in the cargo.toml, then put the resulting binary file in "~/.cargo/bin" (just looked it up to be sure). The user can then either execut from that directory directly or prefix PATH with it in his ~/.profile or similar files, making it available like any other program.
A separate package manager is not remotely needed for this and thus poses an unnecessary dependency and burden on users who didn't have homebrew installed. It integrates with the systems package manager in that it takes higher priority (well, or lower, depending on wether PATH was prepended or appended) during application lookup and does nothing else. Without looking at it I'd guess that homebrew does the same.
> I know almost nothing about cargo since I don't do rust
And you don't have to. Git clone, cargo install, add line to .profile (if not already there), done.
I don't see how any of that is better than brew. There is lots missing from your "no knowledge is needed" stance, like (1) how to install cargo (2) how to uninstall packages (3) how to upgrade them (4) how to install binaries without compiling.
For people who already have brew installed (since it works for much more than cargo) these things are already known.
It works on most distros and for most languages, instead of being tied to, say, rust or arch.