6 hours of downtime is simply unacceptable. I'm a huge fan of Invision, love the amazing software they develop and maintain for us. But when I pay 150/month for a hosted service, I expect more. In 20 years of being self hosted on inexpensive shared hosting services, I've never had more than a few minutes of downtime at a time.
The fact that Invision relies on AWS and that the issue may lie with AWS is irrelevant to us, the customers. As a professional, if I can't deliver a service to my customer because Invision is down, I can't charge my customers. If my forum is down, I can't earn revenue from ads. I can't just tell the customers (or the ad network) "it's not my fault, the software cloud service I'm using was down" and continue to charge them the same amount. I have no choice but to take responsibility and suffer the loss in revenue and reputation.
Invision should take responsibility here, offer $ compensation to paying customers, and deal with whatever service providers they use on their own term. As Invision customers, that's not our problem.