sdkmanager returning the same output, regardless of what arguments are passed to it

I've installed SDK Tools for Windows and attempted to run it; yet, regardless of what I run (sdkmanager, sdkmanager --list, sdkmanager --version, sdkmanager asdoifjasodjfoas) it always prints the same block of text:

Usage:
  sdkmanager [--uninstall] [<common args>] [--package_file=<file>] [<packages>...]
  sdkmanager --update [<common args>]
  sdkmanager --list [<common args>]
  sdkmanager --licenses [<common args>]
  sdkmanager --version

With --install (optional), installs or updates packages.
    By default, the listed packages are installed or (if already installed)
    updated to the latest version.
With --uninstall, uninstall the listed packages.

    <package> is a sdk-style path (e.g. "build-tools;23.0.0" or
             "platforms;android-23").
    <package-file> is a text file where each line is a sdk-style path
                   of a package to install or uninstall.
    Multiple --package_file arguments may be specified in combination
    with explicit paths.

With --update, all installed packages are updated to the latest version.

With --list, all installed and available packages are printed out.

With --licenses, show and offer the option to accept licenses for all
     available packages that have not already been accepted.

With --version, prints the current version of sdkmanager.

Common Arguments:
    --sdk_root=<sdkRootPath>: Use the specified SDK root instead of the SDK
                              containing this tool

    --channel=<channelId>: Include packages in channels up to <channelId>.
                           Common channels are:
                           0 (Stable), 1 (Beta), 2 (Dev), and 3 (Canary).

    --include_obsolete: With --list, show obsolete packages in the
                        package listing. With --update, update obsolete
                        packages as well as non-obsolete.

    --no_https: Force all connections to use http rather than https.

    --proxy=<http | socks>: Connect via a proxy of the given type.

    --proxy_host=<IP or DNS address>: IP or DNS address of the proxy to use.

    --proxy_port=<port #>: Proxy port to connect to.

    --verbose: Enable verbose output.

* If the env var REPO_OS_OVERRIDE is set to "windows",
  "macosx", or "linux", packages will be downloaded for that OS.

I installed sdkmanager from the "Command line tools only" section in https://developer.android.com/studio/. My current version Java is Java 9 (jdk-9.0.1 and jre-9.0.1).

If it means anything, I was having some issues with running the program (java.lang.NoClassDefFoundError: javax/xml/bind/annotation/XmlSchema), so I changed the DEFAULT_JVM_OPTS flag in sdkmanager.bat to set DEFAULT_JVM_OPTS="-Dcom.android.sdklib.toolsdir=%~dp0\.. -XX:+IgnoreUnrecognizedVMOptions --add-modules java.se.ee" which allowed me to run the program without any errors but also lead to the main issue in this question.