Magento 2 Create Controller With No Theme?

I have gathered many controllers that all use different outputs. The first one is the most commonly used and it does interact with the layout. The other can output plain text, json and build your own blocks

use MagentoFrameworkAppActionContext;
use MagentoFrameworkAppResponseInterface;

class Index extends MagentoFrameworkAppActionAction implements HttpGetActionInterface
{
    public function __construct(
        Context $context,
        MagentoFrameworkViewResultPageFactory $resultFactory
    ) {
        parent::__construct($context);
        $this->resultFactory = $resultFactory;
    }

    /**
     * Execute action based on request and return result
     *
     * Note: Request will be added as operation argument in future
     *
     * @return MagentoFrameworkControllerResultInterface|ResponseInterface
     * @throws MagentoFrameworkExceptionNotFoundException
     */
    public function execute()
    {
        return $this->resultFactory->create();
    }

}

// plain response not using any layout

class Alternative extends MagentoFrameworkAppActionAction implements HttpGetActionInterface
{
    public function execute()
    {
        $this->getResponse()->setHeader('content-type', 'text/plain');
        $this->getResponse()->appendBody('this is a plain response');
    }
}

// json response not using any layout

class Alternative extends MagentoFrameworkAppActionAction implements HttpGetActionInterface
{
    public function __construct(
    ActionContext $context,
    MagentoFrameworkControllerResultJsonFactory $jsonResultFactory
) {
    parent::__construct($context);
    $this->jsonResultFactory = $jsonResultFactory;
}

public function execute()
{
    $data = ['test'=> 'this is the response'];

    $result = $this->jsonResultFactory->create();
    $result->setData($data);
    return $result;
}
}

// build your html within the controller

class BlockWithinController extends MagentoFrameworkAppActionAction implements HttpGetActionInterface
{
    public function execute()
    {
        $layout = $this->_view->getLayout();
        $block = $layout->createBlock(MbsAnswerBlockRandom::class);

        $this->getResponse()->appendBody($block->toHtml());
    }
}

// BUild a controller in the backend that outputs a json message: https://bitbucket.org/magstaging/backendcontroller/src