WordPress is ubiquitous. That's an uncontentious statement. When your open source software literally runs a double digit percent of the internet, complaining about how much contribution you get from anyone is really just whining: WP Engine competes with WordPress.com and they're clearly doing well enough to exceed what Automattic puts out for some customers.

Any attempts to introduce nuance around "WordPress hosting" versus "hosting for WordPress" or whatever legally acceptable phrasing satisfies the legal requirements will hurt far more little guys than WP Engine, and stunt the future growth of WordPress as a project. WordPress isn't enterprise software that you buy support contracts for, like ElasticSearch or Mongo. At this point, other than just making noise on Twitter, the only effect any of this will have is putting people off from using WordPress.