The "working around USB for a decade" remark is quite fitting imho
But there's also a versatility benefit to USB being you have options where / when you do your USB to I2S conversion, this however adds to the "messy" appearance.
Most commonly the USB to I2S conversion is performed inside the DAC. MSB offers this as the MSB USB input module. But indeed it's generally accepted that their external MSB Pro USB solution, which moves the USB to I2S conversion to an external adapter, and then transports I2S over an optical link to the DAC, is the superior solution.
This is actually more similar then different to what Wadax offers, both perform their USB to I2S conversion externally from their DACs. But obviously Wadax can place their XMOS module inside their server and go direct I2S over optical out, where MSB needs to rely on that external module for compatibility as they don't manufacture their own server based sources (yet?).