No all L5 systems would need to be designed by those with extensive 'fire engineering' experience.
For example a premises that otherwise needed only manual call points but also a had a fire door electromagnetically held open and automatically closed upon detection of smoke by detectors installed either side of it would be designated L5/M
However, I understand the point being made is that those who don't understand the requirements of categories are trying to hide behind the L5 designation. But since the L5 category is designed to satisfy a specific fire safety objective other than that of a category L1, L2, L3 or L4 system then I don't see how they are getting away with it.
I have noticed recently that almost every premises insurance policy I have seen includes a requirement for at least a L2 system. Whilst I don't agree with the insurance companies just 'guessing' a category as they appear to be doing, the simple fact is that anyone not doing what their insurance policy requires, despite the findings of any FRA, is likely to be uninsured.
I think the first step these days for anyone being asked to design a fire alarm is to ask what the insurance company has asked for. In fact, in the future, I see a role of a professional FRA is possibly going to be as an 'argument' to reduce the insurance companies requirements when the FRA reveals the category demanded by the insurance company is OTT!
With respect to the 'good old days' of fire officers deciding what was to be installed am I the only one who came across numerous poorly designed systems? However, I would agree that maybe the Fire Service should take on this responsibility once again but they should then be able to charge a commercial rate for doing so and have departments of properly trained personnel to do the work to an agreed national standard.