The emphasis on mid range has definitely "gone" and in my opinion the overall quality is not as good as a result. It may sound alright on a high end receiver but most listeners to 648 will probably be in a vehicle where AM reception plays second fiddle to FM and DAB. Here the audio now sounds quite flat and is tiresome to listen to for any length of time. It can be improved by tuning a couple of kHz high but this may not be an option for most users.
The aim should be for the best quality all round and not just catering for enthusiasts with more capable receivers.