RCDs it would seem is a valid problem, as to glands on SWA it does depend on earthing system, sometimes using a stuffing gland is correct, but where the problem lies is coding.
C2 = potentially dangerous. It does not mean does not comply with current edition of wiring regulations, that code was dropped as being unhelpful.
230 volts AC is always potentially dangerous, so it does seem an odd phrase to use, in real terms it means it needs fixing, whereas C3 means you need to be aware if any other work is to be done. So yes the RCD problem needs fixing.
So a consumer unit (CU) is a type tested distribution box, designed to be accessed by ordinary persons. To get the type testing, the units fitted inside it have to have been tested for use with that make and model of CU. So in real terms, a Wylex CU can only have Wylex items inside it.
Where the line has been superseded then we can be faced with changing the whole CU because we can't get the parts, so we do see where to save money a MCB/RCBO/RCD of another make has been shoehorned in.
This makes the CU into a DB as to if it matters, depends on who is using it.
But an EICR is the inspectors personal opinion, it is not like an MOT where there are very well-defined pass and fail criteria. And it is between the installer and the inspector to work out what is safe.