I do think the sound quality is better, but my view is subjective, and could be entirely psychosomatic. That was only partially the reason why I got an Arcana though.  You don’t always have a choice of what audio codec the  content you want to watch is in.  You’re going to get DD+ from streaming sources and TrueHD from discs.  Some game consoles won’t give you atmos in DD+ either.  So using eARC instead of ARC only gives you more options.

Secondary to that, without Arcana, your audio stream is dependent on your TV, which primary function in video, not processing audio.  Thus, the manufacturer is less concerned about audio quality, removing any delays etc.  Removing your TV from involvement in audio entirely is a good idea.

I have a Dolby Atmos demo Blu-ray disc that allows me to test the same content in both Dolby TrueHD Atmos and DD+ Atmos. I tested a bombing/air raid scene from the film Unbroken. I kept the volume level on my Arc/Sub/Play:1s setup the same on both the TrueHD and DD+ test.

The sound was MUCH better with TrueHD. Not only was the TrueHD track louder, it was also more impactful with heavier bass, a bigger sound field, and higher dynamic range. I felt like I was in the bomber plane with the men as they were surrounded by multiple explosions from flak while enemy planes were flying all around the bomber and attacking with gunfire. I felt the danger of the scene MUCH more with the TrueHD track compared to DD+.

This is why I still prefer physical media over streaming. Lossless audio from a Blu-ray disc sounds so much better than lossy audio from a streaming device.