Whenever someone's asking for 8% of
gross revenue, they've lost the plot regardless of the underlying claim. For most businesses that's easily much more they're taking
in profit. One imagines were this agreement in place, WPEngine would have to raise their prices to levels beyond what any customer would pay.
Likewise, the use of "wordpress" as a trademark is clearly permitted when referring to wordpress; it's a common part of trademark law that you can refer to products in this manner. WPE customers do not think WPE is wordpress, it's a host.
cf., "The most trusted platform for WordPress" --https://wpengine.com