It's hard to judge how strong an airframe is without seeing a picture of it.
I have a 36 in Comet Sparky that weighs 7 ounces and it flies great and is a lot tougher than it looks. Trust me I know.
I have a Rocket that is a bit larger, around 40 inch wing and has a flying weight of 12 ounces. It bounces pretty good too.
I smacked the ground with a 7 pound Aeromaster and did a lot of damage.
The more the mass goes up the faster they have to fly and the harder they hit.
So I wouldn't say it is fragile just because it's light.