Wordpress is actually quite horrible product and it produces ridiculously heavy loads even if it doesn't have super crazy plugins and theme. Adding another plugin to "protect" your WP installation makes everything even worse. Yes, it prevents brute force attack (attackers won't be able to use the login/registration form) but since WP is such a heavy platform, it will increase the load even more because there's another layer of PHP code that visitor needs to go through.
Like another person said, xmlrpc.php is another file that is being used for brute force attacks and if you don't use it then there's really no reason to have it available for public.
What you can do is mess with permissions (so that web server cannot read the file and it produces an error page), use htaccess to redirect traffic away to some other site or just block the request and show 403 page. If you can, use WAF (web application firewall). One free and amazing option is to use mod security which these days reasonable web hosting providers install into their servers. If you have your own server then you should install it too. Mod security comes with OWASP (
https://modsecurity.org/crs/) which is a set of rules for mod security for extra protection and it's all free!
During situations like this you want to prevent bots from overloading the server which is why you show them a static page. If you compare 100 requests per second to a static page vs 100 requests to your wp installation that has tons of "protection" plugins.. it's pretty obvious who wins this battle. If you still want to use plugins instead.. try to at least have PHP7.x (it's a lot faster than php5.6+ which is commonly used too).
Htaccess is processed before PHP which is why it's such powerful tool to use. It's not only for overwriting urls and making them pretty