So plugins aren't the answer? So this is in response to using Query Monitor in order to debug a slow WordPress admin? Now, while I agree, adding unnecessary plugins for no reason is not the answer.
This is for debugging. So if you've got a WordPress admin, and in case you didn't realise, WordPress uses plugins. Like, people that use WordPress will use a lot of plugins, and quite often it will result in a slower WordPress admin.
So in order to speed it up, sometimes people don't know which plugin is causing the problem. So by enabling this plugin just for debugging, it'll give you the answers. It doesn't fix the problem for you, it just points you in the right direction.
So in this case, plugins are the answer.