Yes, it is and it's main floor cabin is 27" wider than the 77W's cabin. So if I could choose beween a 10 abreast 777 and a 10 abreast 388, my choice is clear. So clear that I'm willing to pay more for the 388.
BTW the A388 could have slightly wider seats than the 77W even in 11 abreast (3-5-3) configuration.