Just as an aside - in the sidebar on stuff NOT to do there was a recommendation "not to use 2 part epoxy" for structural connections. The example was a composite sunroof insert bonded to a steel roof panel.
It's possible the composite laminate was polyester resin based - not an epoxy layup - and epoxy would not be the right adhesive for the application. It could be poor or incorrect surface preparation, the wrong adhesive, mix ratio or curing condition. There are too many variables to dismiss epoxies summarily on the basis of this failure.
Lots of things are epoxied together that tend not to break. Like F1 cars and jet airplanes, boats and skis and snowboards, that sort of thing.
If you're keen on gluing stuff together (and in my career in R&D in the biotech and renewable energy sectors it happens often) I'd counsel that the nice people at Henkel-Loctite, Sika and 3M have lods of info online and Loctite has a printed guide book series that's excellent. Also the McMaster-Carr online catalog has good adhesives info.