Magento – ny way to delete/remove admin user programmatically

It's the current admin password of the user you are logged in with, not the one you are about to create.

For the first thing If you are using this controller on frontend side then you should extend the Magento\Framework\App\Action\Action class Instead of Magento\Backend\App\Action

And you can use below script to create an user for admin

use \Magento\User\Model\UserFactory;
use \Magento\User\Model\ResourceModel\User;

public function __construct(
       ...... 
        UserFactory $userFactory,
        User $userResourceModel,     
        .....
    ) {
        $this->userFactory = $userFactory;
        $this->userResourceModel = $userResourceModel;
    }

Now you can use this like,

    $model = $this->userFactory->create();        
    $model->setRoleId(7);// change with it 
    $data = array(
        'username' => 'killer',
        'firstname' => 'killer',
        'lastname' => 'killer',
        'email' => 'me@helloworld.com',
        'password' => 'hello@123',
        'is_active' => 1,
        'interface_locale' => ' en_US',
        'role_id' => 7
    );
    $model->setData($data);
    $this->userResourceModel->save($model);