There's no reason that Wordpress couldn't handle this, but it's true that you may have outgrown your current setup. I recently migrated a site with 30K users and 19K articles with legacy 301s for all of them. It was cumbersome, but doable.

You may want to use dedicated hardware, but it all depends on the load and it's probably not necessary. This is definitely the kind of work you want to pay to have done. If you DM me I'll connect you with a firm I worked with to do mine.