SINAD is a small factor for the sound and hardly inaudible, however it’s measurable and considering two AVRs without much difference in functions (like X3500H and X3600H), returning the worse is always the best option. I was confused between Denon and Marantz AVRs because many people say Marantz HDAM circuit makes music better and charge more for that hardly audible feature, but ASR proved that’s nonsense.
Now we look at your example, between a denon 4300 and arcam avr20, they have a very different main factor: Audyseey vs Dirac. The difference is totally audible and bad SINAD performance of arcam is outshined by room correction. Denon is not a better AVR, it’s a better engineered AVR with good SINDAD. If you love Dirac, no need to return it for a better SINAD, however if you don’t use Dirac, there is no way we will pay 2k+ for Arcam.
That’s where ASR reviews come to help your AVR choice before buying expensive stuff for people with limited budget (like me). I’d use up all my money and totally pay for Dirac sound, but seeing the bad SINAD here, I’d hold up money and wait until I see a more reasonable dirac AVR because it may be my last purchase.
However if you’re rich, just buy the best AVR with the best technology and best sound to your ear, and replace by another better one later.
Also, ASR reviews is also a drive for manufactures to do better if they see customer returns their products. Maybe someday we will see an Arcam AVR with better SINAD thanks to armir and all the people in this forum.