It seems to have improved a bit. By no means is it perfect. I test drove another 2014 e class and it shifted much smoother. Mercedes said it could take up to 2 weeks for the adaptations to learn.
You're lucky they were honest in admitting they have no idea what it could be. It gets expensive when they decide to throw parts at an "unknown" issue. I highly doubt 2 weeks of driving is going to resolve the hard downshifts.
Have you by chance checked your motor/transmission/rear sub frame mounts?