It's interesting to consider at least! Afaik FI is more efficient at idle, so ...
Plus the 70-degs are pretty quiet. Muffler design. I like it!
Still I think I wouldn't exactly say my 570 was absolutely quiet when idle. Bigger, higher-compression explosion than in the 390, and it carries quite well from the intake beneath the front of the seat. I actually LOVE the intake sound! A little like Darth Vader as it mechanically gasps for air and then the insistent muffled sound of it working in the midrange, and the scary roar when you open it up to let people hear your bike fun!