How to manage cache issue on toplink in mageno 2?

I am showing logged in username in Magento 2 toplink. But due to Magento full page cache, it showing another username. I tried using cachable=”false” for toplink block. It works on the MyDashboard page but it slows down my home page and other cms pages due to its make cachable false for the full page. Anyone, guide me on how to achieve it?

default.xml

Code for reference(toplink.phtml)

    < ?php if ($this->helper('VendorModuleNameHelperData')->isLoggedIn()) : ?>
    
< ?php echo __('Logout'); ?>
    

    
< ?php echo 'Hi, '.$this->helper('VendorModuleNameHelperData')->getFirstname(); ?>
            ▾
        

            
My
                    Account

            
Return
                    Order
            
        
    
    < ?php endif ?>