Composite models are not better than built up models it is just another form of construction, yes it is easier for those with no skill to get panel lines details etc but there is no reason why any well built and finished built up model can not be the same as a composite one.
Composite is easier/quicker to mass produce and why used, but any well designed built up model is equally or maybe stronger than a composite one.

Snag with composite in regard to strength is it is never guaranteed, once done you have no way of knowing if it was actually layed up correctly without breaking it.
This is one reason why in the fullsize light/ultralight aircraft world many composite designs fail to meet some countries approval, simply because of the unknown of how it was layed up.
Where as in built up, metal, rag & tube etc designs, once the first one meets approval, everyone after that will always be the same and easily examined to check that.