I think that, when you are dealing with HG-PG IQ scores and a child who performs in the avg-high avg range and who appears "in no way gifted" to teachers, 2e is a real possibility. My dd11 is similar. Her WISC-IV scores at around the same age had three subtest or composite HG+ scores (VCI @ 99.7, PRI @ 99, & GAI @ 99.9) and a teacher who said that she was "nothing special." She was sometimes above grade level, but nothing stunning.
Her older sister whose IQ scores are somewhat lower, but still somewhat HG has always been so stunning above grade level in her performance that it is nearly impossible not to notice by teachers and others. 2e or major underperformance due to poor fit would be the two things that would fit in my mind in a sitution like your ds' and my dd's.
For us the things that narrowed it down to 2e and not just checking out/lack of engagement were family history, wildly erratic performance, and never really performing on par with her ability even in areas of interest.
Re him not being far enough behind to be dyslexic, I really don't think that is true with that kind of IQ. My dd, too, has never been below grade level. On a bad day, she's high avg for grade level. On a good day and an individual test like the WIAT or an above level test like the EXPLORE, she can occasionally pop scores that look HG+. Your ds isn't performing on par with his ability. If he wasn't so very able, he'd be way below grade level and the school would see a major problem.
