WordPress.com isn't a good comparison to WP Engine. For starters, you can't install plugins, because you're renting out a single site on a multisite network and any custom plugin code would trivially violate the paper-thin isolation between tenants. WP Engine provides separately containerized servers and databases so you can do whatever.

It's like the difference between getting an account on a Mastodon instance versus a specialized Mastodon instance hoster.