I think that php has some weird disk usage behaviour that makes running Wordpress in a docker environment slow. I don’t know exactly what it is but I would say it is a weird behaviour of php anyway.
Wordpress is just bad. PHP is leader in CMSes but the old ones Wordpress, Drupal have to support so much legacy stuff. Including wierd patterns hand hacks from the past. Modern CMSes like Craft, Kirby, Twill, Bolt, October… it is very different story.
I'm sure the other CMS are fine but I want my site to auto update itself and all its plugins for the next 20 years with me hardly touching it.