So you say we shouldn't benefit from competitor's outages, but we can benefit from their failures of different types? Because every time you claim that you do something better than competition, it's simply you trying to benefit from their failure to do this thing right.
I think the line should be a bit further than you say. Benefiting from someone's downtime or any other kind of failure is perfectly fine, unless that downtime/failure wasn't easily avoidable. If the downtime/failure is because the company lack of professionalism then you should go and benefit from it. If their downtime is because they are hosting servers in their own office, under CTO's desk, and cleaning lady disconnected the cable, shame on them.
That said, this wasn't the case. DDoS isn't something anyone can easily protect from and because of that you shouldn't try to benefit from it. If you do, you basically lie to your customers by making impression that you could avoid such outage.