If you look at the entries, there was no way everyone that deserved to be in the fast heat was gonna get in. Way too many quality athletes. As it is, heat two is a fast heat too.
Michael Atcoo PR 3:39, Mt. Sac Champ 2015
Johnny Gregorek PR 3:39, 5th 2016 USATF Indoors
Colby Alexander PR 3:36, 6th 2016 USATF Indoors, 9th USATF Outdoors 2015
Ford Palmer PR 3:36, 11th 2015 USATF Outdoors, 5th 2014 USATF Outdoors
Peter Callahan 3:37, '15 Flotrack Throwdown Champ over Rupp, Torrence, etc.
Duncan Phillips PR 3:39, Mile 3:56 First non-qualifier '15 USATF Outdoor final
Jordan Gusman PR 3:39 (just last month), Aussie
Hassan Mead PR 3:38 One of USA's fastest 5000 runners in history
Garrett Heath PR PR 3:34 (3:51 mile equivalent)
Leo Manzano PR 3:30, Olympic Silver 2012, US Worlds qualifier 2015
Andrew Wheating PR 3:30, Two-Time Olympian
Dorian Ulrey PR 3:35, former 1500 World Championship qualifier 1500
Pat Casey PR 3:35, Mile 3:52 USATF 1500 runner-up 2014 Outdoor 1500
Maybe you can justify moving a couple of these guys to heat 2 and moving up a couple studs from heat two but as I said, heat two isn't suffering for competition!!