Personally I prefer adding non steam game option. Or better yet, using nonsteamlaunchers to manage all my third party titles under one prefix.

But the point of lutris is to give you more control over where you prefix is, manage your proton version, custom scripts, intall dependencies, and one click installs for most launchers and games that may require workarounds.

That's kind of a basic summary of it, someone else may be able to go into more depth, I haven't used lutris in quite some time.