Well... I guess that should be true. And I´m not saying it´s not. BUT... according to measurements, the Babyface Pro FS is in the same ballpark as cheaper SSL, Audient, Motu... These graphs are from our friend Krause. Take a look at how similar is the RME to the EVO4, and how it is outperformed by several units in every measurement:
Of course, I know that numbers don´t tell the full story... but I´m still to see measurements that confirm the supposed higher audio quality of RME/Antelope/UA interfaces over the cheap brands ones.
Sure, I know about the measurements. I'm going on my experience with various units which were paired with the same monitors and power amp for a number of years until they were finally retired. My first audio interface was a Soundblaster Pro, moved up to an M-Audio Delta 66, and then released how much better things sounded when I used an external DAC in the form of the TC BMC2. From there, all sorts came and went: RME Hammerfall cards, Multiface 2, Steinberg UR22, Motu M4, RME Babyface Pro FS, RME Digiface USB with ADI-2 FS DAC/ADC, the UCXII, even the Yamaha O1X...
The best I had was the Digiface USB connected to the ADI-2 FS converter. I had the Motu M4 at the same time and spent hours comparing them. The bottom end and top end with the MOTU was very good, a marked step above most of the cheap stuff. The RME combo was just better. Soundstage, imaging, clarity, you name it.
I don't have any of that now. I'm sat here with a choice of an IK Axe One and an NI Komplete Audio 6 Mk 2. Why? Because I simply don't need the better stuff right now. One day, I will :)
And you're quite right in saying that the difference between the cheaper stuff and the high end is getting narrower (or words to that effect). The MOTU M4 is a bloody great interface. I know many swear by Audient but the latency figures on their devices put me off.