I2S was pushed by those selling I2S. Trashing USB was a necessary part of this marketing campaign. I have an Innuos that is optimized for USB. I have a Grimm that is optimized for AES/EBU. I like the AES because it is a great connector and there are a lot of good cables available. However, there are now great cables available for USB.
Bottom line, don’t buy a DAC or a Streamer just for I/O options. Use the option that the OEM recommends as they have implemented that option best.
Beware of I2S as there is no standard for implemetation. So your DAC may do it one way and your streamer another.
Jerry
PS both options have been better than SPDIF in my experience, but SPDIF is better than optical.