Well no not really as you are judging them by modern standards. You have to remember they were designed 70 years ago. The most common amplifiers were vales with an output of 10 to 15 watts, transistors were in their infancy. They are no more fragile as any other speaker provided they are used within the manufactures recommended limits. There would not be so many still in regular use worldwide if they were that fragile. Even today many people still overdrive lots of other makes usually damaging the tweeters or failed woofers due to overdrive or clipping a solid state amplifier.
At the time they were designed they were produced to handle about 30 watts which is double what the norm was at the time. It was only many years later with the development of silicon technology did we start to get amplifiers which exceeded that figure. Even Quads 50 watt 303 amplifier exceeded the recommended input for the 57 but protection was added to cater for any potential issues.
The FRED 63 for the US market was called the ESL 63 PRO. It has a much more rigid frame and was fitted with grab handles for the sides. Again it was was widely used in both the professional and domestic markets.