Well, if they are saying that really thin walled bikes with old, extra-light rims are more fragile than modern, then yes. Your Raleigh has neither and should be able to stand up to any reasonable level of abuse you'd care to heap on it. Racing-specific frames, rims and components of old are a different animal. There are steel tube sets and lots of old lightweight rims that are considered only suitable for riders below 150 lbs, etc.